Cougar Tach

[Royce]

I am sure a search would uncover the answer, but I am feeling lazy... How is the tach signal on my 68 Cougar 302 generated?  The last owner just had to go and put a GM 1 wire alternator on it. Now no tach and no electric gauges

[mbrunson427]

Royce, I did the 1-wire on our cougar a few years back. You are able to remove the voltage regulator, but there is still a power wire that needs to be jumpered. I'd take a look at the voltage regulator area and see what they did there. The car is at my house now so I can look at it tonight if you need more info.

[galaxiex]

Ford and Merc factory in dash tachs of that era are current sensing.
Power from the ignition switch goes in series thru the pink resistor wire,
to the tach, and from the tach to the coil positive.

[Royce]

Thanks for the schematic.. Does the input work with 12v or does it need to go through a resistor and drop to 5 or 6

[galaxiex]

Thanks for the schematic.. Does the input work with 12v or does it need to go through a resistor and drop to 5 or 6

I'm fairly sure it goes as described above.

Power from the ignition switch goes in series thru the pink resistor wire,
to the tach, and from the tach to the coil positive.

I'm not 100% sure tho...

Been a long time.... but when I wired my 68 Mustang and added a factory tach in the dash,
I am pretty sure that is how I wired it.
Old guy memory could be wrong....



It worked just fine until I added a MSD 6AL.
Then it needed the MSD 8920 tach adapter to function properly.

[Royce]

I'll give it a try.. That's pretty much how an aftermarket tach is wired

[galaxiex]

I'll give it a try.. That's pretty much how an aftermarket tach is wired

I thought most aftermarket tachs are voltage triggered from the coil negative.

These Ford tachs are current sensing.

Seen very few (really none) aftermarket tachs that are current sensing like the Ford tachs.

Am I missing something?

[Royce]

Ahhh  My bad  I did not notice the coil connection was positive side Not the neg side which aftermarket coils use

[Royce]

Would replacing the factory alternator and bypassing the regulator with a 1 wire unit affect the tach and gauges? None of the gauges are working

[galaxiex]

Would replacing the factory alternator and bypassing the regulator with a 1 wire unit affect the tach and gauges? None of the gauges are working

Gauges and Tach are completely separate circuits from the alternator and regulator.
The only thing they have in common is, they are all electrical devices.

Factory gauges are fed power from the ignition switch.
Factory Tach is wired as in the post above.
Neither have anything to do with the alternator circuit.


Exception if you have a factory in dash Ammeter.

[Royce]

XR7 so there is an amp meter