Starting to work on the 72 I bought from a friend. When he got it 5 years ago it had an HEI distributor in it and the tach worked. He put a stock distributor in it with Pertronix ignition and was never able to get the tach working. I am not sure what I need to do to get it working again. He said he was told he needed to send it to a shop and have some mod done to the tach. The previous owner wired in a kill switch behind the driver seat. I will probably chase that down and remove it, as it kills the coil power. It will crank but not fire with this switch off.
The '72 tach was wired through the points/primary circuit, in series, so if the tach quit, your car wouldn't run. So, you need a '75(?)-'79 tach and harness, in order for it to work with the Pertronix unit. Or, buy an aftermarket one, put it on the column.
There are tach adapters available for just that problem, I know MSD lists several. I would say contact Pertronix and they can tell you what you need to fix it.
I contacted Pertronix and this is their schematic reply. The wire from the tach should be resisted to 7-9 volts from it for the original points/coil. I have 12 volts so somehow the resistor has been removed. I have to get into it to find out where/how the kill switch was wired in. UPDATE: This diagram is for a factory coil. Pertronix now says for their coil keyed 12 volts to coil + then resistor off of coil + to tach wire.
I am having similar problems the tach worked fine, until i started messing with the cluster because of no dash lights I ordered and installed a new Printed circuit and pretty sure that's not the problem. My Tach now starts at 2000 and works from there like normal , so im not sure what i did or how to start to fix it
Try unplugging and inspecting the connector terminals, see if one is breaking or is already broken. The fact it starts reading at 2K makes me think you have a high resistance or broken terminal in the connector.
Thank you, its a pain to pull that apart agian, the terminals look good and after i removed the cluster the tachometer is at 2k with nothing connected to it The needle bounces around with me moving it but never goes below 2K
Going to an aftermarket performance distributor and ignition system for my '75 GT, I gave up and sent my cluster in to Redline to modify the tachometer for what is now a standard tach signal from the ignition system. They also fixed my clock as well. That was years ago and I no longer know with Redline but it was well worth it.
