where's the tach get its signal from?

Cougar Community Classic Cougar Maintenance Restoration and Repair
1

Hey Guy’s
I am wiring up my 67 xr7 now hoping to fire up the engine in a few weeks.
I notice that there is no wire from the distributor side of the coil going to the inside of the car so I assume that the
Tach doesn’t work off of the coil. so what does it use for a tach signal? If it uses the alternator then I have another question
because I have converted my alternator to a 1 wire so I would need to know what wire is the signal wire for the tach?

As always
Thanks
Eric

2

On a 67, the routing for the coil and tach goes as follows:
Ignition plug provides a wire to the tach; the output of the tach goes to a black plug at the junction of the headlight and underdash harness; a second wire at that plug goes back out to the engine gauge feed harness plug just past the firewall; a wire carries the signal to the + side of the coil.

It sounds like you’re missing part of the engine gauge feed harness (oil, water temperature, and coil).

3

What Randy said. Here’s the Ford ‘diagram’ of a factory tach installation

Not shown but important: The wire between the tachometer and the coil includes the ‘pink’ resistor wire. The OEM tach will not function correctly w/o a resistor.

4

Ok, that makes sense.
So since I have now converted my Alternator to a one wire, If I use the wire that came from the battery post of the alternator for my charge wire, will my charge gauge most likely work? The other wires from the alternator and the regulator are no longer used.

5

Probably not. You’re better off converting your charge gauge to a voltmeter. The one big drawback of the one wire alternators…

6

Rocketman sells an awesome voltmeter that bolts right in where the old ammeter lives. Looks like it was born there.