The tach is not working

[grannyknot]

I'm working on a 72 240z atm, it has a standard Pertronix ignition and the engine is running well, no problems there.

Before I tear the dash out I'm wondering if any of these wires will restore the tach, on the coil are the red and black from the Pertronix and one of the black w/white stripe wire going to the positive side. Three wires left over, 1 black w/white stripe, 1 green w/white stripe and 1 black  wire that I thought would be a ground but isn't.

I was going to try connecting the loose wires one at a time to see if I could get it working but I've fried Pertronix units before so thought I would ask first.

Thanks

 

[zKars]

Put all the wires back where you had them on the coil and ballast resistor, (except the black one, that went to the points) then put the new Red/black from the pertronix in place. That way + current to the coil goes through the tach again. Once you get that working, you can try removing the ballast resistor by connecting its two leads together, IF the coil is 1.5 or 2 ohms on its own. Start there.

Just realized you might not know where the three loose wires were originally. Picture coming

 

Edited March 29 by zKars

[zKars]

Green white to ballast, front, long BW to ballast (rear), and short BW to coil +

If you don’t have a ballast, connect the long BW and the GW together.

I’mm doing the same thing to this car today. I’ll let you know if I run into issues

Edited March 29 by zKars

[SteveJ]

This may help, too. 

 

[grannyknot]

Thank you gentlemen, that did the trick, working perfectly now.

[Yarb]

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