FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: cjshaker on June 02, 2014, 07:37:08 PM
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My '69 R-code Mach has a fuel gauge problem that is driving me totally nuts. I did a total rotisserie restoration on it several years ago and my fuel gauge at first would start to work, then it would creep back to empty, fluctuating slowly. It went on like this for a while until it just stopped working. With the engine out I took the time to go through and finish a few details that were bothering me. First and foremost is my fuel gauge.
First, knowing that restorations can lead to bad grounds with painted surfaces, I was careful to double clean all grounds when reassembling the car. I have not had a problem with anything else working because of a ground.
As for the fuel gauge, I checked the sending unit and it is giving good ohm readings at half and full. Right now it reads 15 ohms with a full tank. When I grounded the wire the gauge does not respond at all, so next I went to the dash. I replaced the circuit board and voltage regulator during the restoration, so I looked there first. The circuit board seemed ok but I replaced it with a newer reproduction anyway that seemed a little nicer than the older one I had. No change. All my dash lights and other circuits work but I can't check my other low voltage gauges because the engine is out. The oil pressure and temp gauges seemed to work before the engine pull though, just not the fuel gauge. Although I have Autometer gauges that I depend on for temps and oil pressure, I only have ONE fuel gauge. Of course I checked power to the fuse and the fuse itself. They are good with power coming on when I turn the key.
Since it's nearly impossible to get to the circuit board with the cluster plugged in, and since I have NO confidence in reproduction parts, I replaced the voltage regulator with another one. Still no change, which I expected. Next I tested the gauge itself. It reads about 14 ohms which indicates it is good as all of the low voltage gauges I've tested read the same. I have cleaned every terminal, ground, contact (including the contacts on the circuit board feed AND the circuit board. I can even see the "contact" points where the connector is making contact with the circuit board connections). I have temporarily double and even triple grounded all grounds to make SURE that is not causing my problem.
I noticed in my wiring diagram that it is a resistor wire that feeds the cluster, but when I check the wiring harness "tang" at the plug-in I get 12.6 volts. What is the resistor wire for if I'm getting 12 volts at the plug in? Further, when I pull the gauge cluster out with it plugged into the harness and with the key ON, and with the connector at the regulator unplugged, I get 12.6 volts on the "hot" side of the connector (the 9volt battery type connector). BUT when I plug the connector back onto the regulator it then drops to a millivolt reading?? ??? ???
What gives here? Is my ignition switch giving me a "ghost" reading when a load is applied? I was going to pop the fuse out and feed 12 volts to the gauge side of the fuse and see if that was the issue, but I'm puzzled about that resistor wire in the diagram. A resistor should drop voltage, yet I get full voltage at the cluster plug-in. ??? What suggestions do you guys have to go from here? I apologize for the long post, but this is driving me absolutely insane!! I need to get this figured out before I drive it again (already ran it out of gas once.....and that is ONE TO MANY TIMES!
Thanks for any help you guys can give me. At this point I'm ready to fly in some electrical guru to help me figure this out....if I could afford it. I have never had such a hard time figuring out a problem like this. :( :(
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The gizmo in the tank is good?
They can be quirky especially old ones .
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If the gauge reads empty then it sounds as if the circuit is open or zero volts. What is the resistance of your sender as measured from the cluster plug to ground?
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As for the fuel gauge, I checked the sending unit and it is giving good ohm readings at half and full. Right now it reads 15 ohms with a full tank. When I grounded the wire the gauge does not respond at all, so next I went to the dash. I replaced the circuit board and voltage regulator during the restoration, so I looked there first. The circuit board seemed ok but I replaced it with a newer reproduction anyway that seemed a little nicer than the older one I had. No change. All my dash lights and other circuits work but I can't check my other low voltage gauges because the engine is out. The oil pressure and temp gauges seemed to work before the engine pull though, just not the fuel gauge. Although I have Autometer gauges that I depend on for temps and oil pressure, I only have ONE fuel gauge. Of course I checked power to the fuse and the fuse itself. They are good with power coming on when I turn the key.
Since it's nearly impossible to get to the circuit board with the cluster plugged in, and since I have NO confidence in reproduction parts, I replaced the voltage regulator with another one. Still no change, which I expected. Next I tested the gauge itself. It reads about 14 ohms which indicates it is good as all of the low voltage gauges I've tested read the same. I have cleaned every terminal, ground, contact (including the contacts on the circuit board feed AND the circuit board. I can even see the "contact" points where the connector is making contact with the circuit board connections). I have temporarily double and even triple grounded all grounds to make SURE that is not causing my problem.
I noticed in my wiring diagram that it is a resistor wire that feeds the cluster, but when I check the wiring harness "tang" at the plug-in I get 12.6 volts. What is the resistor wire for if I'm getting 12 volts at the plug in? Further, when I pull the gauge cluster out with it plugged into the harness and with the key ON, and with the connector at the regulator unplugged, I get 12.6 volts on the "hot" side of the connector (the 9volt battery type connector). BUT when I plug the connector back onto the regulator it then drops to a millivolt reading?? ??? ???
I have several comments and suggestions, none of which may lead to a solution, but they may provide a start.
- Measuring the resistance of a gauge is not a good indication that it is functional. The fact that it measures the same as the other gauges is positive, but I wouldn't rule out the gauge as the problem based on that measurement.
- When you checked the wiring harness tang at the plug in, was it connected to the dash cluster? If it wasn't, the only current you would get through that wire is through your meter, and so the voltage drop due to that current, across the resistor in the wiring harness, will be negligible. If you then plug the connector in and only get millivolts at the regulator, there is a whole bunch of current going into the gauge panel, leading to this low voltage at the regulator. Maybe the resistor in the wiring harness has given up and nearly shorted, or maybe there is some other component that is shorted and causing the problem.
With a bunch of different connections it is nearly impossible to debug a circuit like this with everything connected. I would start with the gauge, all by itself, to confirm that it is working. I believe the voltage regulator is a 5V unit; take 3 D batteries, hook them together in series to get 4.5V or so, and power up the gauge with it disconnected from everything else. If I recall correctly with no input from the sender the gauge should read empty. Then, ground the sender connection and see if the gauge goes to full. If it does, next I would try to power up the panel with the voltage regulator disconnected; just power the wire from the regulated side of the voltage regulator, and see if the fuel gauge still works. If it doesn't, you know the problem is in the panel somewhere. If it does, it is either the regulator (doubtful since you have replaced it) or the resistor wire in the harness leading to the instrument panel. Wish I had a 69 wiring diagram; I would kind of like to know the purpose of that resistor. Anyway, hope this helps - Jay
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The book says to take the tank sending unit out and move the lever up and down,
if the gauge moves properly "the sending (gizmo) unit is defective".
If the gauge does not move properly the gauge or wire is faulty.
I still say the gizmo is defective. lol
I have changed two of them in the last 10 years or so because the gauge would not move.
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The gizmo in the tank is good?
They can be quirky especially old ones .
I'm sure the sender is good. 13-15 ohms is right where it should be for a full tank. Resistance is higher for a lower fuel level.
What is the resistance of your sender as measured from the cluster plug to ground?
I cleaned all the connections, but I'll make a long test lead and check this. I don't expect to find a problem here though.
- When you checked the wiring harness tang at the plug in, was it connected to the dash cluster? If it wasn't, the only current you would get through that wire is through your meter, and so the voltage drop due to that current, across the resistor in the wiring harness, will be negligible. If you then plug the connector in and only get millivolts at the regulator, there is a whole bunch of current going into the gauge panel, leading to this low voltage at the regulator. Maybe the resistor in the wiring harness has given up and nearly shorted, or maybe there is some other component that is shorted and causing the problem.
Jay, I thought a resistor dropped voltage, but you're saying that it is based on current draw? In other words, the voltage will not show a drop until it has a load on it? And if there is a short somewhere in the system, then the voltage will drop considerably more than it should? Just trying to wrap my head around what you said.
I would start with the gauge, all by itself, to confirm that it is working. I believe the voltage regulator is a 5V unit; take 3 D batteries, hook them together in series to get 4.5V or so, and power up the gauge with it disconnected from everything else. If I recall correctly with no input from the sender the gauge should read empty. Then, ground the sender connection and see if the gauge goes to full.
Yes, it is a 5 volt system, and yes, it should read empty with no contact (full resistance)....or full with little resistance. I have had my doubts about the gauge and had not considered the battery trick. I will try that first. This may be an issue as my other gauges worked, at least best I remember because honestly I never watched them, just my Autometer gauges. But I DO remember my temp gauge working because I compared its intake probe with the Autometer gauge probe located in my thermostat housing to see exactly when my thermostat opened.
I have a 1969 original dealers ring bound book that covers all wiring/vacuum schematics for Ford and Mercury products in 1969 and there is nothing that indicates what the resistor is for. It is simply in line from the fuse block to the gauge cluster feed and affects or feeds nothing else. Although I can find NOTHING in any Ford manual that says what that wires resistance should be >:( To my knowledge, the resistor is only there to help the regulator live a long and prosperous life ::)
The battery trick to test the entire cluster is a great idea and I will do that.....as soon as I cool off and clear my head...lol
Now that I think about it, I should be able to power up the cluster with the batteries and jumper to the sending unit wiring also to check the entire secondary part of the system. That will break it down into 3 separate systems and isolate which one has the problem. Thanks for jarring my head and getting me to think a little straighter about the subject.
edit: According to a '69 Mustang Concours wiring specialist, the resistance wire should read 9.5-10 ohms. So I can check that also. Ford was definitely in a transitional phase with wiring from '69-'70....and it shows. There are several shortcomings in the '69s wiring system. Some that are down right dangerous to the health and well being of your car. That's why I NEVER leave the battery connected while it's sitting.
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The book says to take the tank sending unit out and move the lever up and down,
if the gauge moves properly "the sending (gizmo) unit is defective".
If the gauge does not move properly the gauge or wire is faulty.
I still say the gizmo is defective. lol
I have changed two of them in the last 10 years or so because the gauge would not move.
I have checked the senders resistance at low fuel level, half full and full. The resistance is correct at all spots, so the sender is not the issue. It was easier to just add 5 gallons of fuel at a time and check it at each level than take the whole unit out :)
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What happens if you ground the sender wire? Does it go full?
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Not trying to start an argument, but it's the sender.
Take it out and wiggle the lever. That's why the book even says to take it out.
Although it is just a potentiometer, it is a gizmo in a tank of gas.
It does funny things.
At the end of the day you can change all the easy parts and new wire and spec everything with the meter.
You will still have to pull the gizmo out. btdt
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When I worked at the Ford dealer in the 70's, this is the test method we used to use:
Disconnect the wire at the fuel tank sending unit. Connect a common test light in series between the end of the sender wire and ground. Turn ignition key to "on." The test light should blink while the fuel gauge moves to full. If this happens as described, the sending unit is faulty. If the light does not blink, the IVR is bad. If the light stays on steady, there is a short to ground somewhere in the wiring. If the fuel gauge does not move to full and the test light is blinking, the gauge is bad.
Hope that helps.
Lou Manglass
proud owner of "The Magic Ratchet"
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Jay, I thought a resistor dropped voltage, but you're saying that it is based on current draw? In other words, the voltage will not show a drop until it has a load on it? And if there is a short somewhere in the system, then the voltage will drop considerably more than it should? Just trying to wrap my head around what you said.
That is correct, this is Ohm's law, pretty much the first thing they taught us in electrical engineering school. V=IR, where V is voltage (V), I is current (Amps), and R is resistance (Ohms).
So, let's say that your wire leads from the 12V battery, through the 10 Ohm resistor, and directly to ground (0V). Then the current through the wire will be (12-0)/10, or 1.2 amps. That's the simple case.
Now let's say that you have connected your voltmeter to the end of the wire, and the other side of the voltmeter to ground. The voltmeter has a very high internal resistance. Let's say for the sake of an example that it is 10,000 Ohms (it is higher actually, but we'll use 10K Ohms as an example). Now, you have a different equation, (12-0)/(10+10,000), or about .0012 amps (1.2 milliamps). So, the current is greatly reduced. How much voltage will you see at the 10 Ohm resistor with only this small amount of current going through it? Voltage drop across the resistor will be (.0012) X 10, or 0.012 volts. So, with your 12V battery, you will see 12-0.012, or 11.988 volts at the 10 Ohm resistor.
I don't know if that helps; it sounds to me like the test light method described above is probably a pretty good one if it works...
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Jay and Doug i have copies of the Ford wiring manual , they cover 69 mustang and cougar . when i was in high school i had a buddy that worked at a ford dealer in parts and gave me the master to copy i had a 1970 cougar back then and a 69 mach now .. you guy s contact me at bn69stang@gmail.com or ( 505 ) 934-4127 and i can dig it out and make some copies and get them to you .. and my 69 did the same thing as yours and it was the sending unit ..Bud
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Jay and Doug i have copies of the Ford wiring manual , they cover 69 mustang and cougar .
Bud, I have a factory Ford wiring and vacuum book that covers all Ford products for 1969. Picked it up many years ago for $5 at a local yard sale of all places. It turned out to be very valuable when I restored my car. Here's a couple shots of it...
(http://i43.photobucket.com/albums/e363/cjshaker/IMAG4859.jpg) (http://s43.photobucket.com/user/cjshaker/media/IMAG4859.jpg.html)
(http://i43.photobucket.com/albums/e363/cjshaker/IMAG4858.jpg) (http://s43.photobucket.com/user/cjshaker/media/IMAG4858.jpg.html)
First, I did as Lou suggested and did the test light test. The light never even hinted at coming on.
Next, I double checked continuity from the plug-in back by the tank up to the cluster plug-in. I got about 3 ohms which seems like a good number considering the footage of wire involved. I checked each connection point (there are 2, a 3 prong plug behind the dash and the single connection in the trunk for the sender wire), visually and by wiggling it to make sure there was no intermittent connection failure.
So I did Jays suggestion next and used 3 D batteries and powered up my gauge cluster. A shot of the battery set-up, minus the leads I used to jumper to the gauges....
(http://i43.photobucket.com/albums/e363/cjshaker/IMAG4867.jpg) (http://s43.photobucket.com/user/cjshaker/media/IMAG4867.jpg.html)
Doing this, I got every gauge to work perfectly. First I went across each terminal on the respective gauges. They all moved nice and smooth with no hesitations. Second, I went to the primary side of the regulator on the circuit board then to the secondary side of each gauge. Again, they all worked smoothly. That told me that the circuit board and the regulator seemed to be working fine and was making good connection at all points.
At this point I figured the resistor wire feeding the gauge cluster was bad. But before I condemned it, I played around with the gauges some more to see if I had a short somewhere causing the voltage drop from the resistor wire as Jay suggested might be the case. This is where I got confused again. I got a continuity reading from grounding to the metal cluster housing, then to each terminal on every gauge. This, to me, indicated I had a short somewhere and that that would cause the voltage drop from the resistor wire.
I took all my gauges out and inspected them. All isolating pads are in place as they should be, and in good shape. I even checked to make sure they did not give a continuity reading through the isolation pads. A shot of the pads on the back of the gauges, and the ones that go on the outside of the cluster to isolate it from the housing....
(http://i43.photobucket.com/albums/e363/cjshaker/IMAG4868.jpg) (http://s43.photobucket.com/user/cjshaker/media/IMAG4868.jpg.html)
This one just showing the pads without the gauges being installed....
(http://i43.photobucket.com/albums/e363/cjshaker/IMAG4870.jpg) (http://s43.photobucket.com/user/cjshaker/media/IMAG4870.jpg.html)
Next, I checked for continuity from the regulator to the cluster housing. First from the regulator housing to the cluster housing. I got good continuity as I should have. Then I checked on the primary and secondary side of the regulators terminals to the cluster housing. I got 12.78 ohms on the secondary side....then 4.27 ohms (yeah, ironic huh :) ) on the PRIMARY side. I thought BINGO, I have a short in the regulator! It shouldn't be reading from the regulator terminals to ground.
WRONG. I checked the schematic.....
(http://i43.photobucket.com/albums/e363/cjshaker/IMAG4874.jpg) (http://s43.photobucket.com/user/cjshaker/media/IMAG4874.jpg.html)
As you can see, the primary and secondary sides of the regulator seem to be connected to the regulator housing, or ground. So the numbers I got appear to be normal. This also explains why everything worked fine when I powered through the regulator.
So now I am wondering why and how this works. When I jumper the positive side of my batteries to the cluster HOUSING, then connect the negative to the secondary side of the gauges, they work. This just doesn't seem right to me ??? But I am not an electrical engineer, so I may just be wrong. Am I simply feeding power through the ground, into and through the regulator (essentially bypassing it) and on to the gauges? According to the schematic, that seems to be the case.
IF this is normal, then my issue is with the resistor wire feeding the cluster. So now I need an engineer to tell me if this is normal per the schematic.
Is there a Doctor in the house? :)
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Thats the same ford manual that my copies are out of , but just have the electrical part of it - but $ 5.00 well spent lol and it looks and sounds like its driving you crazy .. GOOD LUCK Bud
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Same question as My427stang, "What happens if you ground the sender wire? Does it go full?"
If it does go full then I would say it is the sending unit.
If you want a further test ground the sender wire through a variable resistor and watch the gauge go up and down.
I believe ScotiaFE is correct, it is going to be the sending unit.
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Same question as My427stang, "What happens if you ground the sender wire? Does it go full?"
If it does go full then I would say it is the sending unit.
If you want a further test ground the sender wire through a variable resistor and watch the gauge go up and down.
I believe ScotiaFE is correct, it is going to be the sending unit.
That was the very first test I did. I mentioned it in my first post, but it was kind of long so I think you guys just missed it. The gauge did not move when grounded. And when performing Lous' suggested test, I could not even get the light to come on. So I am positive that the sender is not my issue.
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This is a great suggestions, "If you want a further test ground the sender wire through a variable resistor and watch the gauge go up and down". Or you could just get a few resistors & test with those in place of sender. Sounds like there is an open in the circuit/wiring between the gauge & the trunk. Run a new wire from the sender to the gauge, if all works you just need to find your open.
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This is a great suggestions, "If you want a further test ground the sender wire through a variable resistor and watch the gauge go up and down". Or you could just get a few resistors & test with those in place of sender. Sounds like there is an open in the circuit/wiring between the gauge & the trunk. Run a new wire from the sender to the gauge, if all works you just need to find your open.
As I said before, I tested the wire from the sender clear up to the cluster plug-in. It is good. I even tried running a jumper wire from the wire off the plug-in to ground to eliminate that entire harness to the tank. Still nothing. Using a variable resistor in the senders wire would not be any different than trying it to ground. If the gauge will not move with it grounded, then it won't move with any resistor in the line.
I do know a little about electronics, although when I get frustrated I tend to forget the simple things. Like when Ohms Law was mentioned from Jay. I used to work on kitchen cooking equipment which had plenty of electronics, and I tinker with working on my own tube amplifiers, but I am no expert by any means.
At this point I'm thinking the resistor wire feeding the gauge cluster is faulty, but I was hoping somebody could confirm/disprove my thinking on the regulator terminal/ground readings I got. The regulators schematic seems to suggest (to me) that it basically works like an alternator regulator, but on a much simpler level. I just don't know enough about the electronics involved as to whether or not it is a physical connection to ground inside the regulator which would explain my ground readings and why the gauges work when powering through the clusters housing.
I tried disconnecting the regulator at the posts and the gauges do not read when powered through the housing. That confirms that power is traveling through the regulators housing, feeding the gauges. I think I need to rig up a 10 ohm resistor wire and feed it to the cluster while hooked up to the main harness and see if the gauges work then.
Edit: I'm having my Dad bring down some wire-wound 10 ohm resistors to rig up a feed for it. I'm not sure if carbon resistors will handle the load. He went to DeVry University in the '50s for electronics. Actually made my Grandpa and Grandmas first TV and had his own TV and Radio shop when he was young. He's got tons of old electronic equipment, but at 84 he's gotten kinda bad at remembering some stuff. It's not good that I have that same problem at my age ::)
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At this point I figured the resistor wire feeding the gauge cluster was bad. But before I condemned it, I played around with the gauges some more to see if I had a short somewhere causing the voltage drop from the resistor wire as Jay suggested might be the case. This is where I got confused again. I got a continuity reading from grounding to the metal cluster housing, then to each terminal on every gauge. This, to me, indicated I had a short somewhere and that that would cause the voltage drop from the resistor wire.
Next, I checked for continuity from the regulator to the cluster housing. First from the regulator housing to the cluster housing. I got good continuity as I should have. Then I checked on the primary and secondary side of the regulators terminals to the cluster housing. I got 12.78 ohms on the secondary side....then 4.27 ohms (yeah, ironic huh :) ) on the PRIMARY side. I thought BINGO, I have a short in the regulator! It shouldn't be reading from the regulator terminals to ground.
As you can see, the primary and secondary sides of the regulator seem to be connected to the regulator housing, or ground. So the numbers I got appear to be normal. This also explains why everything worked fine when I powered through the regulator.
So now I am wondering why and how this works. When I jumper the positive side of my batteries to the cluster HOUSING, then connect the negative to the secondary side of the gauges, they work. This just doesn't seem right to me ??? But I am not an electrical engineer, so I may just be wrong. Am I simply feeding power through the ground, into and through the regulator (essentially bypassing it) and on to the gauges? According to the schematic, that seems to be the case.
IF this is normal, then my issue is with the resistor wire feeding the cluster. So now I need an engineer to tell me if this is normal per the schematic.
Is there a Doctor in the house? :)
Just so that we are using the same terms, when you say the primary side of the regulator, you mean the input side, right? The side that gets the 12V through the resistor wire? Then by secondary you mean the output side, where the gauges get 5V?
The regulator is connected to the gauges, and the gauges are a resistive load. When you check continuity, you are talking about checking resistance in Ohms, so from the output of the regulator you have several resistive loads (the gauges) in parallel, running to ground. So, you should get some resistance level when you make that check, and 12 Ohms is certainly not out of the question.
The fact that you are getting a lower resistance from the input side of the regulator to the ground is kind of confusing, but may be possible depending on the design of the voltage regulator. However, if you are powering up the steel housing of the gauge panel with 12V, grounding the gauges, and they work, I think there has to be a short somewhere. Ford wouldn't have powered up the steel housing of the gauge panel.
One other thing that dawned on me was the connector. If I recally correctly '69s have a pretty marginal connector to the circuit board, don't they? I seem to recall that the connector wasn't indexed in place real well, and it might be possible to move it around and potentially short two of the traces on the circuit together. Maybe a ground and an input power? Sure wish I was there to look at this for you, Doug...
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Just so that we are using the same terms, when you say the primary side of the regulator, you mean the input side, right? The side that gets the 12V through the resistor wire? Then by secondary you mean the output side, where the gauges get 5V?
The regulator is connected to the gauges, and the gauges are a resistive load. When you check continuity, you are talking about checking resistance in Ohms, so from the output of the regulator you have several resistive loads (the gauges) in parallel, running to ground. So, you should get some resistance level when you make that check, and 12 Ohms is certainly not out of the question.
The fact that you are getting a lower resistance from the input side of the regulator to the ground is kind of confusing, but may be possible depending on the design of the voltage regulator. However, if you are powering up the steel housing of the gauge panel with 12V, grounding the gauges, and they work, I think there has to be a short somewhere. Ford wouldn't have powered up the steel housing of the gauge panel.
One other thing that dawned on me was the connector. If I recally correctly '69s have a pretty marginal connector to the circuit board, don't they? I seem to recall that the connector wasn't indexed in place real well, and it might be possible to move it around and potentially short two of the traces on the circuit together. Maybe a ground and an input power? Sure wish I was there to look at this for you, Doug...
Yes, I should be saying the "hot" or "input" side and "load" side referring to the regulator terminals. Wrong terminology can confuse things for sure.
I added a picture of the regulator in the schematic. Not sure if you saw it or not, but it shows the connections to the regulators housing, which is grounded through the PCB. The connections to the housing are not only on the load side, but also the input side. According to the books symbol chart, this is a thermal switch that regulates the voltage. Much like the alternator regulator.
The regulators schematic....
(http://i43.photobucket.com/albums/e363/cjshaker/IMAG4875.jpg) (http://s43.photobucket.com/user/cjshaker/media/IMAG4875.jpg.html)
Symbol chart....
(http://i43.photobucket.com/albums/e363/cjshaker/IMAG4876.jpg) (http://s43.photobucket.com/user/cjshaker/media/IMAG4876.jpg.html)
As you can see, there is some variance from the books symbols to the actual regulators schematic. The symbol shows it being an external heater where the schematic shows an internal type, but with external "graphics". Not sure if it uses a bi-metal switch or some other type. Being DC it can't be based on cycles.
I certainly wouldn't think the housing would be "live" either, but the heater seems as though it could back feed when I apply voltage to the housing. And if the switch is closed that would complete the circuit making the gauges powered.
I have inspected the entire set-up six ways from Sunday and can not find where a short could occur or IS occurring....other than through the regulator itself. And according to the schematic, that is by design for the heater.
And to FURTHER complicate things, with every gauge disconnected from the PCB, and with them REMOVED from the cluster, I get a continuity reading from every gauges post to its respective housing. As if every gauge is shorted to its housing. This is just not right, and I can find no trace of why it should be shorted (as I said, each gauge has its internal and external "isolator" pad)....yet I still get continuity.
I also thought about the plug-ins indexing, and checked it. You can see in this picture that the connections seem to be squared quite nicely with there respective contact....
(http://i43.photobucket.com/albums/e363/cjshaker/IMAG4866.jpg) (http://s43.photobucket.com/user/cjshaker/media/IMAG4866.jpg.html)
When I start looking for the sledgehammer as my next tool.....it's time to walk away and take a break. And that is very much needed right now :-[
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I had the same problem , and started checking things because i was leaning towards a gauge but it ended up being a bad sending unit ..
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I'm not sure if you guys get the idea that the gauge wont read even when the sending units wire is grounded. The sender does the same thing. It "varies" the grounding that occurs. The more grounding that the sender does, the fuller the gauge should read. One of the first checks to do for a sender is ground the wire itself, if the gauge starts moving then your sender is bad. If the gauge wont read with the wire fully grounded, I fail to see how the sender will make any difference.
But anyway, enough about the sender. It is not the issue.
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Doug go have a cold one , unwind before sledge hammmmmering operation starts ... Bud
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Doug go have a cold one , unwind before sledge hammmmmering operation starts ... Bud
Now that is advice I can adhere to :)
I did not mean to come across as unappreciative. Just very frustrated right now. Thanks for everyones help.
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OK, let's assume that the wiring in the dash is all OK. Seems strange to me that Ford would put voltage on the instrument panel chassis, but maybe I'm missing something there. One thing that could cause your problem is if the resistor wire went high in resistance. Then, when the gauges tried to pull current through the resistor wire, the voltage would drop to some very low level. I think you were seeing something like that with one of your earlier tests. Measure the resistance from the end of the resistor wire, where it attaches to the panel, and the instrument cluster fuse. If the resistor is in between there you should see some resistance level, probably only a few ohms. I think it is a 2 amp fuse for that wire, correct? So if 2 amps is the maximum current, and you need at least 5V at the regulator to make it work properly, then the resistor should be (12V - 5V)/2 amps, or 3.5 Ohms. If you measure a resistance much higher than that, then the resistor wire has increased in resistance, and when the instrument panel tries to pull current it is pulling the voltage way down, to far down for the regulator to work. I think temporarily it would be OK to run a wire directly from the fuse panel to the instrument panel, with no resistor in the wire, to check for correct operation. Maybe use a 50 foot length of wire so that the resistance of the wire itself is significant. Once connected, flip on the key and see if your fuel gauge works.
If that's not it, its the sender ;D ;D ;D
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Doug go have a cold one , unwind before sledge hammmmmering operation starts ... Bud
Now that is advice I can adhere to :)
I did not mean to come across as unappreciative. Just very frustrated right now. Thanks for everyones help.
One thing is certain, with the wealth of information that's been presented in this thread we've got a comprehensive approach to troubleshooting a crabby fuel gage system. I am one of several I'm sure who are looking forward to hearing the final solution. I can appreciate the level of frustration at what is seemingly a simple setup >:(.
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yes the problems that just hang around and frustrate the heck out of you , and this forum does help to sort them out , so from me many thanks to the forum .. Bud
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Sheeesh...must be something going around, now my fuel gauge is acting up. :-[
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Sheeesh...must be something going around, now my fuel gauge is acting up. :-[
Yeah maybe so ???. Mine stays right on full until I've got roughly 6 to 7 gallons left in the tank. Once it starts dropping it drops like a stone to under a quarter of a tank and then sits there and dares me to believe it. I for my part do not. I decided it works well enough for now, not sure how things would go on a road trip. That's why I look forward to seeing what it takes to get Doug's gage to tell him the truth....
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For Lenz and mlcraven.
An inexpensive and easy test is get a sending unit and plug it in. Non Mustang units always cost more, but most Mustang units
will fit and do the job. Hope this helps.
https://www.mustangsunlimited.com/itemdy01.asp?T1=9275B+01&Category=Air%2FFuel&subCategory=Fuel+Related&SubSubCategory=Fuel+Sending+Units&CatKey=EMUSTANG
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Lenz I had same problem on my Galaxie
I tock out the sender and exersiced the
arm back and fort to get rid of the oxidation
(that built up while it was not driven for many years)
in the variable resistor and now it working
fine
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Doug, just getting back here, sorry I missed that it wasn't pegging when grounded. So..
1. It doesn't peg when grounded, so it isn't the sender (assuming it was a good connection and good ground)
2. With a test light connected and verified good ground, you should get a dim flashing. If you don't it's either wiring/connection/printed circuit or a bad dash voltage regulator
3. If possible follow the sender wire up and make sure it isn't pinched, melted or grounded, also look at bends that could show that it broke inside the insulation. Just had an ABS system drive me crazy and that was what it turned out to be
4. With the dash off the Mustang, can you get a test light to the back of the gauge? It should have the same flashing current, if not maybe remove the gauge and see if you can access its connections. Once side of the gauge should have resistance to ground, the other should have the flashing source from the VR
5. VR failures are relatively common as are printed circuit failures, new VRs are solid state vice mechanical so they last longer, so I am leaning that way
In the end, the simple circuit is 12V hot to VR, that voltage to sender which is a variable ground. That's it.
Notice I am less concerned with resistance and more concerned with presence of 12V. IMHO beyond an open circuit, resistance only determines accuracy of the gauge, in this case, we need to figure out why no power to the sender, which means a test light will be your friend
One last question, is the factory oil pressure gauge working? If yes, then printed circuit or wiring problem for the fuel circuit, if no, odds are VR
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Howie, Heo, thanks for the tips, much appreciated. I'm gonna sidestep here, not my intent to pollute this thread with a separate issue.
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It was the sender!!
Just kidding ;D ;D ;D
I got it figured out. First, I want to thank everybody for trying to help me. Sometimes electrical issues can just be hard to isolate when multiple systems are involved in 40+ year old wiring. And the '69 and later cars are just more prone to problems when they got away from hard wiring circuits.
I did get it working. I had to go to Detroit Thursday and in between dodging Michigan potholes and dodging cars in roundabouts, the drive up and back gave me time to think about it. I was making it harder than it needed to be by second-guessing my findings. A couple notes....
1: Getting continuity and making the gauges work by running the batteries through the cluster chassis was merely a result of back-feeding through the regulator. I thought that may have been the case, but second guessed my findings. The Constant Voltage Regulator schematic clearly shows the connection to ground for the internal heater. That connection also allows voltage to flow back and into the regulator and through the internal switch and onward to the gauges. I should have just went with what I knew and saw but I made it much more difficult by second guessing myself. I realized this when I had some time to think about it.
2: After checking every connection, wire, gauge and ground I knew that left only a couple of options. The old Sherlock Holmes quote definitely applies here..."when you have eliminated the impossible, whatever remains, however improbable, must be the truth". There were only 2 possibilities left. 1, the resistor feed wire was going bad and losing its ability to hold a load, or 2, the ONLY connection that I could not physically check while hooked up was faulty.....the main harness connector to the cluster.
I decided to physically jumper from the harness to each gauge. So I set the cluster in the middle and jumpered from the correct lead on the main harness connector to the gauge POWER feed connection on the PCB. That way it was going through the regulator as it's designed to do. Then I grounded each gauge individually.
Heres a couple shots of how I did that.
(http://i43.photobucket.com/albums/e363/cjshaker/IMAG4905.jpg) (http://s43.photobucket.com/user/cjshaker/media/IMAG4905.jpg.html)
(http://i43.photobucket.com/albums/e363/cjshaker/IMAG4906.jpg) (http://s43.photobucket.com/user/cjshaker/media/IMAG4906.jpg.html)
(http://i43.photobucket.com/albums/e363/cjshaker/IMAG4907.jpg) (http://s43.photobucket.com/user/cjshaker/media/IMAG4907.jpg.html)
I was careful so that each jumper wire did not touch any other connector lead. And each one worked! YAY!! ;D ;D So then I ran a jumper from every gauge to ground simultaneously to see if the main harness' resistor feed wire would hold the load of all 3 gauges working at their highest reading. That places the highest load on the resistor wire feed and regulator that it would see in the real world. A bit of a warning here, you wouldn't want to hold them all straight to ground for any extended period or you run the risk of burning out the windings in the gauge, but a short grounding of each gauges feed wire at the sensor or sender will tell you if they are working properly. Heres a shot of my jumper wires on the back going to ground and the feed wire hooking to the PCB.
(http://i43.photobucket.com/albums/e363/cjshaker/IMAG4908.jpg) (http://s43.photobucket.com/user/cjshaker/media/IMAG4908.jpg.html)
They all worked!! DOUBLE yay!! ;D ;D
So it HAD to be the main connector to the PCB. I was careful to clean both sides of the connections with polishing paper and made sure none of the connectors spring "tangs" were flattened. I even checked to make sure of imprinting on the PCB connections to make sure there was contact, which I showed a picture of earlier. But as it turns out, when I inspected them very closely, the imprints were a little faint on a few of the PCBs connectors. So I polished everything again and pried out slightly on all the main harness' connector tangs, making sure they had a good arch and spring to them. Then I made sure the PCB was centered perfectly on the housing and plugged in the main harness.....hit the key...and here was the result....
(http://i43.photobucket.com/albums/e363/cjshaker/IMAG4909.jpg) (http://s43.photobucket.com/user/cjshaker/media/IMAG4909.jpg.html)
So just to make sure my sender was good, I pulled the ground off of my tank sender wire, hooked it back up to the sending unit on the tank....and here was the result....
(http://i43.photobucket.com/albums/e363/cjshaker/IMAG4909.jpg) (http://s43.photobucket.com/user/cjshaker/media/IMAG4909.jpg.html)
Notice anything familiar? And yes, it does have a full tank of fuel :)
So I spent the next hour watching the fuel gauge as I jostled, shook and generally beat on the dash unit trying to simulate scared passengers shaking in the car ;D ;D It still worked. So I put everything back together finally. DONE!!
I have to say though, I think this winter or early next year I'm going to rid myself of that PCB and hardwire my cluster like the older cars were. '69 was the first year for the PCBs and they are a pain. You just don't have those problems with the earlier cars with individual wiring to each spot.
One last thing. Anybody with a '69-'73 Mustang knows how dim the dash lights are and how hard they are to see at night. I took the opportunity to try out an LED dash light kit, but only on my main clusters dash lights. Not the clock or the turn signals or anything else, because they are bright enough. I have to say, they made a BIG difference! They are MUCH easier to see, keep the same hue as the original lights, and aren't too bright as to overpower the overall look of the cluster. I really like them, although I had to fiddle quite a bit with the wires on the LEDs to make them get good contact, I really like them as an upgrade in the dash.
(http://i43.photobucket.com/albums/e363/cjshaker/IMAG4902.jpg) (http://s43.photobucket.com/user/cjshaker/media/IMAG4902.jpg.html)
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Howie, Heo, thanks for the tips, much appreciated. I'm gonna sidestep here, not my intent to pollute this thread with a separate issue.
Lenz, you're not polluting anything....unless you're driving a chevy ;)
There's no need to buy a sending unit just to test if it's bad or not. The test for a sending unit is easy, just run a wire from the sending units feed wire (at the tank) to ground and see if the gauge starts moving up. It should do it smoothly and moderately quick. If it does move, the sender is not doing it's job and is faulty. If the gauge does not move.....see above ;D
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Thanks Doug, I'll put the test on my to do list :D. Glad to hear you got it resolved, from what you describe retro-wiring to an older version sounds like it would give you some peace of mind. From everything I've read including your disconnecting the battery when you aren't using the car certainly betrays a sort low confidence level in the current setup. I'll go plus one on second guessing yourself too ???. I've had times when I've charged right past what I knew to be true to complicate an issue. The only way to get it right is to mentally backtrack until you get that "eureka!" moment. So then, on to the next challenge..... ;D.
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Great detective work, Doug, and glad you got it working! I never did like the way Ford did those connectors on the 69 dash. Even with the high quality connectors available in today's cars, if you talk to any automotive electrical engineer who works on wiring, they will still tell you that connectors are the primary failure points of most systems, and that they go out of their way to eliminate as many connectors as possible.
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I still think it is the sender.
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Me too. ::)
Great stuff Doug.
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I still think it is the sender.
LOL! I was about ready to chuck the whole fuel gauge idea and go to the old Model T gauge system. A stick ;D
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So it was the sender huh , all that work to take the interior apart .... lol glad you got it , how many beer s did it take ? .. Bud
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So it was the sender huh , all that work to take the interior apart .... lol glad you got it , how many beer s did it take ? .. Bud
I really wish it had been the sender. It would have been diagnosed in about 3 minutes. On the plus side, I was wanting to change to LED dash bulbs and run a braided line to my oil pressure gauge anyway ::)
Actually I don't drink beer, so I just translated that into Tequila. Worked out pretty well...lol
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Glad you got it fixed , if your bored come over and help tear mine apart .. lol Bud