On my '68 Shelby, the voltage at the same coil wire was much less than 12 volts, so I couldn't use it for pertronix. On my 69, it was over 12 volts, so I used it. Not sure how the "resistor" wire works, I thought it was supposed to reduce the voltage to the coil to below 12 volts, but that is not the case on my '69 shelby. If you have 12 volts at start and run position of ignition switch, it should work fine.