I have an '83 280zx. Where does the tach get it's signal from?

 

The negative side of the coil, I would assume. Unless the tach is controlled by the ECU, which is unlikely.

 

Our tachs are way off to tell the truth. Well atleast mine is. When I dynoed my car I watched the tach on the dyno and watched my tach. The tach in my car was considerably lower than what the dyno was showing. Just thought i'd throw that in.