Are you having issues with your turn signals? They are on the same circuit.
Have you actually tested for voltage? It sounds like you haven't since you don't know what wire.
Just to be clear, while you claim the 3 wire tachometer is from a 240Z, it is not. It is probably from a 260Z. It may have been modified to work on a 240Z in the past. Unless you are the first owner of the car the tachometer came from, you can't know everything that was done to it.
I suggest you read through this: Tachometer Swap : 280z into a 240z series 1 housing
It was written up by someone who used to post a lot here. blue
Have you actually tested for voltage? It sounds like you haven't since you don't know what wire.
Just to be clear, while you claim the 3 wire tachometer is from a 240Z, it is not. It is probably from a 260Z. It may have been modified to work on a 240Z in the past. Unless you are the first owner of the car the tachometer came from, you can't know everything that was done to it.
I suggest you read through this: Tachometer Swap : 280z into a 240z series 1 housing
It was written up by someone who used to post a lot here. blue
