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 Monday at 06:52 PM2 days by cgsheen1

I would like to clarify that

On 9/5/2025 at 5:11 PM, cgsheen1 said:

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.)

I dont know the specifications of this msd blast 2 coil. I do know it did solve the rough idle and the misfire issue when coming out of a long traffic jam. Its connected to the pertronix 1761 module installed in the stock hitachi distributor. Just wondering if this msd coil compatible with this petronix module in anyway?

Couldn't help you with that, but I doubt either part would keep the tach from operating if it's wired properly (the tach and coil) . And if it's running - and running well - why would you think there might be an issue between the MSD coil and Pertronix module? The distributor module (Pertronix, points, 280ZX "matchbox", whatever) gathers info from the crankshaft and sends a "signal" for the coil to fire. It momentarily asserts a Ground on the coil "-" terminal. The rotor "distributes" the released coil energy to the various spark plugs at the appropriate time. If any of that isn't working properly there would be no well running engine.