The wiring for a
typical standard ignition engine typically has an ignition coil marked
"For use with external resistor."
Note that a wire runs from the starter "I"
terminal to the coil side of the ballast resistor. This wire feeds 12
volts directly to the coil when cranking the engine. The purple wire
feeds 12 volts to the ballast resistor which in turn reduces the
operating voltage to the ignition coil. This is important to reduce coil
temperatures and extend the useful life of the points and condenser.
