Special GMC "Resistance Wire"

[FetchMeAPepsi]

I just read this in an old rag and thought Id share. GMCs from the 60s and 70s had what they call Resistance Wire running to the negative side of the coil. it was white, textured wire and was about 48 inches long. It was made to knock the voltage from 12 volts down to 6.1 - 8.8 volts. Thats the right amount to keep the points running long.

To replace it you can use a regular wire and a ballast resistor (Borg Warner part # RU4, Napa part ICR13) but itll get hot and won't last forever. You can also get a donor wire from most any GM 60-74 vehicle. The wire is textured and easy to recognize once you know what to look for.

If you want to buy resistance wire you can pick up some Nichrome at amazon or ebay and measure it out to the right length to get the right resistance depending on how thick it is. Use some voltmeters. Then you need to insulate it good with heat resistant cloth insulation.


If you have changed over to a petronix or other HEI system you shouldn't have the resistance wire anymore. Be a pal and sell it to someone that does.
Now you know more about resistance wires than you ever thought you would.

[WDShaffer]

That post is award-worthy! I ran my '61 and replaced points every 6 months...well every time I got stranded. All because a PO "fixed" an ignition problem with regular wire.

Thx Fetch!

[tommyduncan]

Good info but not just a GMC thing. Anything with points has some form of resistor to accomplish this. Some makes used a little off white rectangular looking one that usually screwed to the firewall.
There is another wire that goes from the starter to the negative side of the coil also. This is to supply the ignition with a full 12+ volts during startup. It only works when the key is turned to the start position. This wire is often removed because people assume it does nothing.