That's what I thought thanks might be time to upgrade . If I go to a 3 wire I just connect the the 2 white wires together right?

That's what I thought thanks might be time to upgrade . If I go to a 3 wire I just connect the the 2 white wires together right?

Correct.

What year and month was your z made.? Mine was 6/73 and it was the three wire tach style. Had me confused for the longest time. There is a thread on here on what I did as well and a thread about swaping the tach too.

On 7/17/2012 at 1:14 PM, beermanpete said:

The 4 wire tach (240Z tach) uses a current sensing circuit on the positive side of the coil. With the original points type distributor the +12V (black wire) connected to the ballast resistor. The green/white wire runs from the other side of the ballast resistor to the tach. The black/white wire returns from the tach to the positive side of the coil.

To get the tach to work you need to connect the solid black wire to the green/white wire (remove the black wire from the coil) and connect the black.white wire to the coil.

It is possible that the E12-80 system will not provide the 4-wire tach with the correct current pulse wave-form to get a reading from the tach. In this case you will need to use the 3-wire (280Z tach). The 280Z tach gets it s signal from the negative side of the coil so you will need to re-configure the wiring appropriately to make it work.

My mechanic replaced a pertronix 1.5 0hms coil and 1.5 resistor coil with an MSD Blaster 2, 3 ohms coil. He got a better spark at idle and car runs much better. The thing is the stock 72 240z tachometer doesnt work any longer. Can someone give us directions on how to connect this correctly so it works as it did?