Depends if you have a points distributor or an HEI. Points run on less than 12 volts, 6-9. The wire from the firewall terminal block to the distributor is a resistor wire which reduces the voltage. I seem to remember Chevs having a ballast resistor instead of a resistor wire. Points distributors use 12 volts to start, which is supplied to the distributor via the starter using the yellow wire. HEIs use 12 volts to start and to run, a switched 12 volt wire is used in place of the resistor wire.
