I have an 82 and an 84 300d. Tach on 84 works ok, tach on 82 doesn't. The 82 has the front pickup and the black cylinder on left fender wall. 84 picks up on rear of engine, no black cylinder on left fender wall. I've tried all the cigarette butt tricks in the 82 cylinder fitting.

The question is, are the gauges interchangeable? Would the 82 work in the 84 if all else were ok. If, for example, I take out the gauge from the 84 and put it into 82 and still doesn't work and the 82 into the 84 does work, then I know its the circuit to the gauge, not the gauge itself that is failing.

Thanks for any help.