2 hours ago, w3wilkes said:

Thanks for the reply and it does make sense. Maybe I'll see if I can find another tach or a replacement smoke kit. Hopefully Lucas parts would be compatible with our Z cars!

Sorry, that is positive earth smoke. It won't work on our negative earth cars.

On 9/6/2025 at 2:45 PM, 72 Datsun 240z said:

My mechanic finally solved the 11 year old problem by resdjusting the carbs with the temperature of the car during traffic jams, 3/4 of the Temp gauge and an MSD blaster coil. Now he is asking me for a diagram or schematic to get the petronix 1.5 coil and 1.5 ballast resistor running and the 1972 240z tachometer working alltogether. Can seem to find it in the web or haynes manual. Do you have any reference for this? Guess the stock tachometer wont work with the MSD blaster 2 coil.

You can download the Factory Service Manual for every year of Z car at nicoclub.com

( https://www.nicoclub.com/datsun-service-manuals )

Coil specs: Engine Electrical EE-26. Electrical Schematic: Body Electrical BE-5

I described the wiring for the tach operation above but:

The coil gets battery voltage at Ignition ON through a Black/White wire. Black/White is a Nissan standard throughout the Z cars of the 70's for "battery voltage (or whatever the alternator delivers) when the ignition switch is in the ON position. NEVER assume a Black/White wire in a Datsun has anything to do with GROUND - IT DOESN'T!

BUT - the 240Z Tach works on amp draw. SO, the tach needs the B/W that powers the coil to run through it (the tach) FIRST (before it feeds the coil).

A ballast resistor was common for ALL single coil distributor engines of that era.

Nissan designed the circuit so that power to the coil when through the BALLAST before the tach and coil. That's why the wiring is a bit confusing.

IN THE STOCK CONFIGURATION, There are three (3) wires that make this happen: TWO Black/White (B/W) wires and ONE Green/White (G/W) wire that are in the harness bundle that pass in front of the radiator core support and then through a hole in the left side and end up in the coil area. (The coil and the ballast resistor are side-by-side)

IF all three of those wires are temporarily disconnected. ONLY ONE of those two B/W wires will have power at IGN ON. Stock config: The B/W with battery voltage would attach to one side of the BALLAST. The Green/White (G/W) would attach to the OTHER SIDE of the BALLAST. The G/W returns to the TACH. From the Tach, the SECOND Black/White (B/W) RETURNS to the COIL "+" terminal.

(IF you were eliminating the ballast for some reason, the B/W with power should attach to the G/W so it feeds the tach before sending power to the coil through the second B/W...)

THUS: B/W from IGN Switch -> BALLAST -> G/W back to TACH -> B/W to "+" side of COIL...

Edited 5 hours ago5 hr by cgsheen1