When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I have a '77 with an HEI distributor and I'm looking for help identifying the wiring from the HEI "tach" wire output on the distributor. Last weekend I put AFR heads on it and when we dropped the distributor in, a wire broke off. The wire is very faded but I think it's tan or brown with a black stripe. It went from the "Tach" side of the distributor, to the firewall and into the tach (I assume). About a few inches from the distributor, the wire became a thick rectangle shape (about 1/4" thick and about 2" long). When it broke off, I lost the "thick" part of the wire. The wire then went into the firewall and I assume to the tach. This is NOT the tach filter as I already replaced that. I have power to the tach but it does not work w/o this thick part of the wire. I have called every Corvette shop I can find and nobody can ID this "thick rectangle shaped part of the wire". I read a forum post that said it may be a capacitor for surge suppression, but nobody I spoke with ever heard of such a thing. I am also afraid to just solder in a new wire to bypass the thick part,
as I am afraid I will blow the circuit board for the tach. Does anyone have any suggestions?
On my 77 I only have 1 brown wire coming coming from that clp. It goes to the tach filter, out the other end of the filter and through the firewall.
Yup thanks. My connector had a brown wire and this weird wire together. I just hooked up the brown wire and the tach seems to work fine. My brother is an ASE certified mechanic (and Chevy guy) and he had never seen a second wire coming out with the brown wire either. I still have no idea what the other wire did though!
This image shows the original wiring configuration for the HEI tach. Note the pink wire...that may be the wiring that is unidentifiable.
Pink should be the battery wire on the BATT output part of the distributor, which I already have connected. I actually had 2 wires coming from the TACH output, which is very weird as every other HEI distributor only had 1 wire. Thanks for ur pic and the info!
To me, your tachometer wiring looks cobbled together.
Your Brother should open up a GM service manual from the era.
The original tachometer filter wiring was simply line in & line out...
Later over the counter GM filters included a service port...
Me thinks that thicker 2" long piece may have been part of the original tachometer filter wiring that broke off at the filter.
To me, your tachometer wiring looks cobbled together.
Your Brother should open up a GM service manual from the era.
The original tachometer filter wiring was simply line in & line out...
Later over the counter GM filters included a service port...
Me thinks that thicker 2" long piece may have been part of the original tachometer filter wiring that broke off at the filter.
I removed the mystery wire and got rid of all of it and the tach works perfectly. I have also spoken to numerous mechanics that had never seen the “thicker” wire and didn’t know what it was. I’m not too worried as I cleaned up the wiring and everything works like it should! Thnx tho
'77 Tach wiring issue
