Recently swapped my 1.5 ohm Petronix Coil and 3.0 0hm resistor with a MSD Blast coil with no coil. Car runs much more better and does not hesitate on traffic jams. Problem is tachometer is not working. How can i fix this?

Do you mean you replaced the Pertronix with the MSD Blast and no resistor? When we replaced the original coil and resistor in my car with a Pertronix and no resistor the tach wouldn't work. I added a TachMatch device. It didn't fix the problem initially, but the entire setup mysteriously began to work almost a year later. It's possible that the tach would have started working again without the TachMatch, but the scenario you've described is one of the use cases for it and mine's continued to work perfectly all summer.

1 hour ago, davewormald said:

I added a TachMatch device.

You didn't mention which TachMatch Device you installed? I did a ZX matchbox distributor with removed resistor on my 12/70 car. My tach almost works but doesn't seem to go any higher than about 3500 RPM.

Here's the wiring for the E12-80 and the TachMatch's for 240s. Mine works great with Blue's Tech Tip ZX swap so I've got no issues in this.

Blue's ZX swap...

TachMatch's diagram. You'll have to open in another window. I couldn't figure out a way to copy/paste for side by comparison.

240ZTachMatchWiring.pdf

13 hours ago, davewormald said:

Do you mean you replaced the Pertronix with the MSD Blast and no resistor? When we replaced the original coil and resistor in my car with a Pertronix and no resistor the tach wouldn't work. I added a TachMatch device. It didn't fix the problem initially, but the entire setup mysteriously began to work almost a year later. It's possible that the tach would have started working again without the TachMatch, but the scenario you've described is one of the use cases for it and mine's continued to work perfectly all summer.

Let me explain this better. My mechanic is trying to fix rough idle issues when my car is at idle during long traffic jams. He removed the Pertronix 1.5 ohm coil and the 1.5 ohm resistor connected to a Pertronix ignitor 1711 module, and installed an MSD Blaster 2 coil. The tachometer in my 1972 240Z is no longer working? Any ideas of how should i wire this so it brings my tach back to life.

Edited Thursday at 01:06 AM2 days by 72 Datsun 240z

On 9/2/2025 at 7:56 PM, 72 Datsun 240z said:

Let me explain this better. My mechanic is trying to fix rough idle issues when my car is at idle during long traffic jams. He removed the Pertronix 1.5 ohm coil and the 1.5 ohm resistor connected to a Pertronix ignitor 1711 module, and installed an MSD Blaster 2 coil. The tachometer in my 1972 240Z is no longer working? Any ideas of how should i wire this so it brings my tach back to life.

Not without knowing how your mechanic rewired your Z. Post pictures of the coil and ballast resistor wiring and the wiring coming back through the radiator core support to the coil and ballast.

Although not uncommon at the time, Nissan used a Tach and wiring method not used in the later Z's - only the 240's. To make the Tach operate, the wiring starts at the ignition switch and winds all the way to the ballast resistor (a Black/White wire). From there they use a Green/White wire to go BACK to the tachometer, through a loop (stupidly simplistic explanation), and then BACK to the "+" side of the coil with ANOTHER Black/White wire. IF your mechanic omitted any of that, changed any of that, your tachometer will definitely NOT work... Your tachometer "reads" the amount of electrical current going to the coil to operate and in it's stock configuration it needed to go through the ballast before going to the tachometer and before finally powering the coil... If he just powered the coil, tach is dead.

(Three wires here in stock config: 2 B/W, 1 G/W. If all are disconnected, the one B/W that has Battery Voltage when the ignition switch is in the ON position is initially attached to one side of the ballast resistor, the G/W is attached to the other side of the ballast resistor. That wire returns to the tach. From the tach the SECOND B/W wire goes to the "+" coil terminal. You can attach that FIRST B/W to the "+" coil terminal and the engine will run, but you've then bypassed the wiring to the tachometer.)

@cgsheen1 Maybe you can help with my tach. After my mechanic did my zx distributor in my 240Z all was well for some time so I guess it's wired correctly. Then one day I was out for a drive and watched the tach all of a sudden start climbing and in a few seconds it had gone all the way over to 8. I shut the car off and sat for a minute then started it back up and ever since it doesn't go above about 3500 RPM. My ballast resistor is removed. Other than that my car runs just fine. Any ideas, maybe a coil change? There's no marking on my current coil so I don't know what ohm it is.