tach wire and a yellow wire
 

I'm trying to figure out what wire is the tach wire(what color) and i have a yellow maybe tan wire under the hood thats hot with key one that i can't figure what they go to.

original, factory, tach SIGNAL wire is Tan. Not too many things are original or factory 40 yrs later though! Hope that helps.

Brent

Thanks i'll give it a try.