How do I Wire a Ballast Resistor & Coil?

by Tracy Underwood

The typical automotive ignition system prior to 1974 consisted of a coil and ballast resistor, with breaker points to interrupt the current flow when a spark was needed. The job of the ballast resistor was to inhibit current to a level that would not overheat the coil. This simple system is easy for even the novice mechanic to wire. So if you have a classic car with missing ignition components, don't hesitate to replace the coil and ballast resistor yourself.

Step 1

Disconnect the negative terminal of the battery, if there is one installed on the car.

Step 2

Route one end of the wire from the engine compartment into the passenger compartment. Strip 1/2 inch of insulation from the end of the wire and crimp on a ring terminal. Connect it to the ignition terminal of the ignition switch. Route the other end of the wire to one terminal of the ballast resistor. Cut the wire, strip 1/2 inch of insulation and crimp on a terminal. Connect to the ballast resistor.

Step 3

Cut a piece of wire long enough to reach from the other terminal of the ballast resistor to the "Bat", "+" or "B+" terminal of the coil. Strip 1/2 inch of insulation from each end of this wire and crimp a connector onto each end. Connect the wire to the unused terminal of the ballast resistor and to the previously identified terminal of the coil.

Step 4

Locate the small gauge wire that comes out of the body of the distributor. Connect this wire to the negative terminal of the coil.

Reconnect the negative terminal of the battery.

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