Adapter for HEI Ignition with Aftermarket Tach? - ClassicOldsmobile.com


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Old March 20th, 2017, 01:31 PM   #1
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Adapter for HEI Ignition with Aftermarket Tach?

Hello all,

I'm new to this forum so immediately I apologize if there is a thread already on this that I wasn't able to find. I'm in the process of restoring a 1970 442 W30, and I'm not exactly sure what I need to do with the Tach. I purchased the aftermarket Rally Pac gauge set from The Parts Place, and the guy on the phone said I might need an adapter for the Tic Toch Tach since I have a Pertronix HEI ignition (see ignition pics below - this came with the car when I purchased it). That said, I haven't been able to find this "adapter" for sale, or that I even need one.

Is there any reason this won't work with (1) the 1.5 amp fused wire from the right post of the tach connected to the negative side of the coil (2) the orange wire for the clock feed and (3) the grey wire for the lights? Any help is greatly appreciated!
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Old March 20th, 2017, 02:07 PM   #2
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Have you just tried running your signal wire to the coil negative post of the coil? That works for most with a Pertronix points replacement ignitions. It is not an HEI.
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Old March 21st, 2017, 08:15 AM   #3
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Pertronix is not HEI. HEI is GM's brand name for the coil-in-cap system and the HEI has a TACH output terminal that mimics the normal tach attachment signal on a point-style distributor. You'll have to ask Pertronix what they recommend, but frankly, the external coil works the same whether it is triggered by points or an electronic system. The negative terminal of the coil must see the same pulse either way to generate a spark. The only time an adapter is required should be for multi-spark systems like MSD that will confuse a tach. I have a similar electronic conversion in my 62 wagon (not by Pertronix, however) and I simply connected the tach to the negative terminal of the coil.
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Old March 21st, 2017, 09:22 AM   #4
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Got it, thank you very much! We (myself and my father who is actually doing all of the real work on the car) are on our 2nd tach. I wasn't there when the first one was installed as I described above, but it sounds like it was a faulty tach. Hopefully we have better luck with this one.
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