Does anyone know if the tach guage on an 82 and 84 are interchangeable. My 84 (no amplifier on the wheel well and rear engine pickup) works fine. My 82 (amplifier on wheel well and front engine p/u) doesn't work properly.

In trying to diagnose, I intend to swap guages (after checking front pickup condition) but since the 84 hs no separate amp in the circuit, I'm thinking it may not work with the 82 input circuit.

I'e tried the cig butt trick (and used foam etc also) in the amp. Haven't tried resoldering anything in the amp.

thanks