Topic: 8K tachometer in 1979 Trans Am issue

[79_455]

Greetings!

So I've succeeded in reparing most all wiring issues in my 1979 trans am ...I run a MSD and have an autometer tach but would like the 8k factory tach i put in to work as well.

What Ive done is use a new circuit board made for the older 8K tach..74-78 board 1st style from firebird central. Everything works great on it.

I see that the tach has 2 pins on it for a harness... one is 12V and another is Tach signal. Dont have my original tach harness, but ive seen on some dash shots a pink wire and white wire that go into the harness above the column .. anyone know exactly what they are? im imagining the pink one is hei tach and the white is some kind of 12v power? 

Does a tach need 12v to run? or does it run just from the tach signal? If it runs just from the tach singal then the 12v must be for clock?

http://firebirdtransamparts.com/techinfo/harness/harness.htm

To prevent taking everthing apart, I was thinking of taking  the 12V pin on the factory tach to Keyed ignition and tach signal straight to MSD which should work....... but i'm thinking this will make the clock only work when the ignition is keyed on?  kinda defeats the purpose... If i recall the clock should always even with no key.

Does anyone know how the tach was wired for a 78? as opposed to a 79 newer style 6k. I dont have any schems for it.. It seems as if that 12v should be going to battery ( which im thinking that white wire was)  if the clock was to always keep time?

Thanks!
Den

[78w72]

not sure on your other questions, but the power wire to the tach is connected to the fuse block power terminal, the other wire is to the hei tach.  msd should have instructions for how to hook up a factory tach.

a 78 is wired the same as 79 with a 6k tach.  8k was done in 75 or 76.

[79_455]

Would you know if the fuse block power terminal is switched 12v? or battery?

Again, im concerned about the clock... Dont know much about it.

Thanks

[78w72]

i cant say for sure but i think its constant 12v.  i can check next time im at my car.  also, the clock is not powered by the tach wires, the tach must take 12v power to work. 

[79_455]

Finally checked all schematics... The clock runs off battery from one of the pins on the cluster harness.

Thanks!