I know the tach won't work with the 12v HEI, but what adapters are available to get the voltage back down, so it works? As in the title, it's a mid 80's HEI installed on a '67 400. Thanks.

I use my hood tach with an HEI.

Oh, well, it must be toast then. A guy at PY was saying that I needed an adapter. So, just ground it and run the hot from the tach spade on the cap to the tach? It lights up, but doesn't sweep.

Yep, that's the way I hooked mine up. It is an aftermarket hood tach. That could make a difference.

OK, so is there any way to test the hood tach to see if it's inop? As far as I know, it could be the original, dealer installed tach. I can get a repop from Year One and such if I have too. No adapter needed then, at least for a repop?

It would be best to check with the manufacturer of the hood tach to make sure it's compatible. The parts houses change suppliers. It's the only way to be safe.

I have an original and it just vibrates a bit with the pertronix setup, I have not tried it yet, but the Pertronix guy said to try different resistors inline. I have the email at work so cant post the exact resistor size till Monday. Sure hope it works for mine tho...

OK, let me know what you find. I'll ask the guys over at PY too. I think they used the same tach on GTO's and Lemans's. So, if I understand this right, I need to get back to the voltage that was produced with the old points distributor? Thanks.

I have a partial MSD ignition set up and had to use an MSD adapter. BUT, I know some of the parts houses sell a specific Hood Tach "Adapter Wiring Harness" for hooking it up with an HEI dist.

Ames part #: 00515 $8.00

Might be just the ticket...

Brett - 67 Drop Top 455!

I have an aftermarket hood tach and have used it with three different HEI systems, including the early GM HEIs. All worked fine.

Nash, the problem is not with the aftermarket ones, it's the originals that tend to like to work with only points set ups....at least in my case....

Eightime.....here's what Pertronix emailed me back with;


"First, double-check all of your connections. A poor ground can do this. Next, feel the entire length of the sense lead to make sure the wire is not broken. We’re looking at 40 year old wiring. If all of that looks good, insert a 10K ohm, ½ watt resistor between the coil negative terminal and the tach sense lead. That should correct it. "

In my case my wiring harness is new, so will have to locate a 1/4 watt 10,000 ohm resister (must have some old radios hangin around somewhere....) I think it would be a brown black orange striped.

I have about 1000 NOS resistors...if I find one in my box, it's yours. 1/4w I have, not so sure about 1/2w.

Have you opened up the tach yet, to see if any wires were bad, or maybe broke of the soldering??

I meant 1/2 watt, but 2-1/4 w ones in parallel would work...I'll bet a 1/4 might work, at least long enough to tell you if the fix works.....

No, I have not opened my particular tach, yet...figured I'd try the easy route first, then open it up.