Hi guys. I have a 76 with a electric tach. Doesn’t work, replaced tach board had a burn on the original one. Still doesn’t work. Have voltage at the wire coming out of the distributor cap (brown) and the filter is missing so I purchased a new one haven’t installed it yet but would like to trace down the wires and see what’s going on. Any ideas what color wires on the tach and what each is for, there are 3 wires attached to the tach board. any help will be appreciated.

 

Not sure of differences between a 76 and an 80, but here's a photo of the circuit board on mine. Pretty simple as far as what the wires are, battery (12 V), ground, and coil.


'80 tach PWB

As far as colors my 80 manual says pink with black stripe for bat, white for coil, black for ground. On mine though I think the coil was brown.

As you can see from this shot of my 40+ year old board, there is a lot of delamination. Coupling that with the closeness of some of the traces there may be intermittent high resistance shorts between some circuits. By high resistance I mean low enough to mess up a signal but not so low as to cause a full blown short of the type that causes arcs. On the other hand it could also have an open somewhere in a trace, a small split that is difficult to detect.

I'd start by simply verifying you have 12 V at the bat screw on the board with ignition in run and that you have a good ground. Then, if so, I would check continuity from the tach connection on the distributor cover to the coil screw on the tach. Leave the capacitor out of the circuit for that. You'll need to temporarily the two wires it sits between. If all those are good then it's in the board, either a trace that's open, a short between traces, or a component failure.

Good luck,