Temp gauge always reads hot.

[428Marauder]

Sorry if this has been covered. I'm too lazy to search.

When ignition turned on, gauge goes all the way too hot, as it should. Stays that way once started. I replaced the sender with a Intermotor TS24 from Summit. It came with some teflon tape on the threads, which I left on. Fortunately I have a spare gauge if it comes down to it, but I have no idea how to open that dash. I've tried.

[Lenz]

Hmmmm...  Either an open circuit (seems more likely, don't know if the sender you bought is compatible?) or a short to ground.  Don't recall 60's FoMoCo products burying the temp gage when you turn the key on, maybe someone else knows if that's the case?

A wiring diagram and search are probably in order unless you've got a pinched or broken wire under the hood.  Of course, you could always buy an aftermarket temp setup and change it over. 

Even so, the buried gage should be figured out.  On the outside chance it is a short things could go badly.  Even though you don't want to pull the dash apart, take a peek at what you can see from beneath.  Is it fairly clean or does it look like a lot of cutting and splicing has been going on?

[machoneman]

Why not get a good and always accurate mechanical gauge and ignore the OEM unit?

[mlcraven]

Sorry if this has been covered. I'm too lazy to search.

When ignition turned on, gauge goes all the way too hot, as it should. Stays that way once started. I replaced the sender with a Intermotor TS24 from Summit. It came with some teflon tape on the threads, which I left on. Fortunately I have a spare gauge if it comes down to it, but I have no idea how to open that dash. I've tried.

I've just gone through the electrics on the 67 Cyclone -- a bunch of small things includng lights (ext, interior, idiot) and gauges.  Although I'm with machoneman (get a good-quality  mechanical gauge) if you're as anal as I am you'll want your original gauges to work as well.  It was my discovery that EVERY LAST ONE of my electical issues was traced back to a ground issue. 

Did this problem start recently, after you did something else to the electrical system?  Have you or anyone else been playing around under dash, new stereo or anything? Sorry I can't be more specific in helping with your problem, but my solution was to go back to first principles with a circuit tester and multimeter.  I'm no electrical genius, like to think of it as marbles rolling through pipes.  And in our negative ground old cars all the pipes have to end at the body or frame.

[428Marauder]

It's been this way since I bought the car. Foolishly I figured replacing the sending unit would fix it. Next is the oil pressure sending unit. Will report back when that is in.

Also I should note that I recently removed, rebuilt and replaced the fuse box, and that fixed none of my gauge issues. Currently gas, temp and oil do not work, or do not work correctly.

[cjshaker]

The gauge should not go to hot when you turn the ignition on. It should come up slightly if its warm out or just stay put until the engine starts to warm up. As the engine coolant warms up, the temp sensor gradually sends the voltage signal to ground, in effect creating a "shorted" circuit. The gauge then basically reads the amount of "short" that the sensor conducts to ground....the warmer the coolant, the bigger the short and corresponding higher reading on the gauge. So if your gauge reads fully hot either the sensor is sending full signal to ground or there is a short someplace in that circuits wiring, thereby fooling the gauge into thinking the sensor is reading hot coolant and doing it itself.

Since none of your other low voltage gauges work,  it sounds like you may, instead, possibly have a faulty voltage regulator on the back of your gauge panel, or you do in fact have a bad ground someplace which can create all sorts of wacky problems. Problems like this are not always easy to track down. You have to start with every ground (and there are LOTS of small grounds to check on a gauge panel), making sure they are in fact getting a good ground to the chassis, then check voltage output of your panel regulator and go from there. I don't believe your car has a circuit board unless it's a '69 or newer, but I'm not familiar enough with your specific gauge panel to comment further without giving some bad info.

[428Marauder]

It's a 65 Mercury Park Lane. I don't even know where to start looking for bad ground connections.

[Wreckless Warren]

What happens if you remove the connection at the sending unit while the engine is running? If the gauge stays pegged wouldn't that indicate your problem was up the line somewhere? ww

[jmlay]

Or the sender is not grounding thru the sealer on the threads. This can be tested by shorting the outside of the sender, NOT THE WIRE CONNECTION, to the intake with some wire or a screwdriver & having someone watch the gauge.

What happens if you remove the connection at the sending unit while the engine is running? If the gauge stays pegged wouldn't that indicate your problem was up the line somewhere? ww

[Lenz]

As a side note, it seems like with all the issues a wiring diagram might come in handy, either from a shop manual (the best overall bang for the buck) or a simpler wiring only manual if one exists.  If nothing else, it provides you with the correct colors, makes tracing a lot easier.

[cjshaker]

Or the sender is not grounding thru the sealer on the threads. This can be tested by shorting the outside of the sender, NOT THE WIRE CONNECTION, to the intake with some wire or a screwdriver & having someone watch the gauge.

What happens if you remove the connection at the sending unit while the engine is running? If the gauge stays pegged wouldn't that indicate your problem was up the line somewhere? ww

If the tape was stopping the ground, his gauge would not register at all. He has the opposite problem.

And yes, a wiring diagram can be a big help....if you know how to read them

[Lenz]

And yes, a wiring diagram can be a big help....if you know how to read them
[/quote]

Quite right on that    I found a single sheet laminated color coated diagram for my Galaxie at Dearborn classics, the thing is actually right!  Went there this afternoon to see if I could provide the holy grail for the '65 Merc, got the "no match found" response. 

I've searched before and two things held true for me.  An ohm meter to check continuity and a thorough assurance that all grounds are good.  As has been stated earlier in this thread, a bad ground is almost always the culprit.  Up here in the salted great white north I need to redo the grounds on my trailers almost yearly.  A bad ground not only messes with the misbehaving circuit, it screws up a lot of other things along the way.  BTW, do you have a ground strap from your 428 to the firewall?  The engine and drive train sit on rubber mounts and I get the feeling that not much is original in your deal, it's a one-off hot rod.........

[428Marauder]

The ground to the firewall is connected. I have a wiring diagram, but it might as well be in Russian, because I'm an idiot when it comes to electrical stuff.

[My427stang]

If the needle pegs, there is a short somewhere between the gauge and the sending unit.

I'd start by unhooking the wire from the sender and ensuring it doesnt touch anything, if it still goes to full hot, trace the wire back until you find the issue, if it doesn't go to full hot when disconnected, you have the wrong sender or a bad sender

[TimeWarpF100]

Sorry if this has been covered. I'm too lazy to search.

When ignition turned on, gauge goes all the way too hot, as it should. Stays that way once started. I replaced the sender with a Intermotor TS24 from Summit. It came with some teflon tape on the threads, which I left on. Fortunately I have a spare gauge if it comes down to it, but I have no idea how to open that dash. I've tried.

There are 2 types of senders one for gauge and one for light.

As others have said the easiest way to trouble shoot is remove wire to sender and turn key to on. Gauge should not go up.
If that is ok then with key still on touch sender wire to ground, gauge should go all the way up.

If gauge goes up all the way with key on wire grounded the sender is the issue. If gauge goes up with wire off gauge and key on then its gauge or that wire is grounded. Is it a white with red or red with white wire?

Also double check if you have proper wire.