Factory tach + painless harness = ?

[Blue Oval Man]

It is my understanding that Ford wired their tachs differently than aftermarket tachs. I am putting a painless harness in the 68 and can't find anything on how to wire the factory tach.
Is the factory tach compatible with the painless harness?
Also, if I do decide to upgrade to aftermarket guages sometime in the future, would the wiring for the factory tach them be compatible with the aftermarket tach?
David.

 

[suki243]

Well, I've never had a factory tach, and have never installed it, but the wiring diagrams that i've seen for it are the same as any other tach wiring.

One wire getting power from the fuse box, one wire going to the ignition coil, a wire for the light and i believe it a ground somewhere.

Here's my source:
http://midlife66.com/wiring/66acces1.jpg

Then again that is the wiring for a 66.

I'm not aware of any other way to wire a tach, For gauges you definitely need a power source, and power for the light, a ground of some kind and a wire to transfer current for watever you're measuring, in this case the tach.

Either way, painless should accommodate it. I used Ez wiring and it is really easy to do, I doubt painless is much different.

Just my two cents.

 

[BarnStang]

Take a closer look at the graphic posted. The tachs are wired in series with the ign circuit. If you unplug the tach, the car will shut off. If the tach fails, the car will shut off. It's a very odd circuit that Ford designed. THe power from the switch in the Run position normally goes through the pink resister wire then to the positive terminal of the coil. With the factory tach, the power leaves the ign switch in the Run position, goes in the tach, out of the tach, through the pink resister wire, then to the positive terminal of the coil. You can duplicate this circuit with the painless kit, will just take some thinking to sort it out.
I have never used a Painless kit though. I tear the original harness apart and rebuild it. My business partner has one in the ProStreet race car, but it came tat way when he bought the chassis. Man, I spent some hours figuring all that out.

 

[Blue Oval Man]

Thanks. Man, it looks like I have some work to do!
Maybe I should just upgrade to the aftermarket stuff right away, sounds like I would have to redo the harness anyway if I do it at a later date.
David.l