4 wire to 3 wire tach

[ricksaia]

Hello all, has anyone out there changed the tach from a four wire to a three wire in a 1970 240Z? Could you let me know how you did the wiring. I installed a distributer and a coil from a 1983 ZX. Of course my tach stopped working. I have the three wire unit, I just need to know how to wire it. Cannot find it anywhere in the forums. Please help. Rick.

[Arne]

I'm a little perplexed on this, Rick. I have the same '83 ignition on my 10/70 240Z with 4 wire tach, and it works fine. How do you have the coil wired?

[ricksaia]

Arne, I used the coil from the ZX and bypassed the ballast resister by connecting the black/white wire to the green/white wire. I don't know why it is not working. So I want to use the 280Z tach, but I don't know how to wire it. Enrique, do you have any input?

Thanks, Rick.

[Arne]

Some more questions, Rick.

1.) I assume that the car is running OK, just no tach?

2.) On the ZX coil - you should have a wire from each terminal of the coil going to the twin terminal connector on the distributor box, and the other black/white wire connected to the + terminal of the coil. So two wires on the + and only one on the - terminal. All sound right?

[ricksaia]

Correct, black/white to positive and black wire connected to nothing.

[Arne]

Odd. That sure sounds like my setup, which works fine. I guess it might be time to swap in the later tach. Wish I could help on that.

[ricksaia]

Appreciate the help. I am sure someone out there has done the swap and will be able to assist. Thanks again, Rick.

[ricksaia]

Anyone swaped out the tach, please help. Rick.

[ricksaia]

I reversed the positive and negative leads on the tach. Then connected a wire from the negative side of the ZX coil to the pole on the tach. Worked like a charm. Hopes this thread helps someone in the future. Rick.