Ballast Resistor Why?

Primary intent of a Ballast resistor, is, to limit the current going to the coil. Reducing the voltage, is a secondary effect.

Ballast resistors are related to the coil, not the type of ignition system (whether points or electronic).

Ballast resistors change their resistance as they heat up, they run hotter at slow engine speeds, thus limiting the current to the coil stopping the coil from overheating at low speed. As engine speed increases, so does the current as the Ballast resistor cools down, to keep the spark voltage high.

Most systems have a bypass while cranking feature, to ensure good voltage to the coil when the battery is not at it's best.

Most British cars didn't use a Ballast resister (not one you could see), as, it was already incorporated in the coil, until about 1970. About that time, they went to a resistor wire, and, 12v bypass system to improve starting in cold climates.

These early Ballasted coils are known as 12 volt coils. Ballast resistor coils are 8-9 volts rating.

Prolonging point life was the job of the condensor, not the Ballast resistor. The condenser is there to reduce the voltage spikes (arcing) that would otherwise eat the points.

Al(BWA)