Explain the purpose of the ballast resistor.

by Herbert Pacheco
(Harbor City, Ca.)

The ballast resistor was used on older points and condenser as well as electronic ignition systems. They were designed to add resistance to the circuit to cut back on current flow in the primary ignition circuit to the ignition coil while the vehicle was running.

During engine cranking, when the battery voltage is pulled low due to demand, the ballast resistor is bypassed so the necessary current flow through the ignition coil can be achieved.

Both General Motors and Chrysler used ballast resistors in their systems. Chrysler used a dual ballast resistor assembly which was a common failure as well.

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