I'm replacing my old beat up tach with a new one. Heres the problem, the old one has 4 wires coming out of it & the new one has 3 wires coming out of it. Anyone know why that is? Also the wire harness on the new one is alot shorter.

 

one possibility, they could have two power wires on the old one. one for the light and one for gauge. the new one could be useing a single wire for both. I have seen this on some gauges that I have installed. just a geuss. I could not find anything in the shop manual.

 

Thanks busmechanic, I think that is it.