Ballast Resistor Guide - Ballast Blast-Off

The electrical system of an automobile is likely the system understood the least by most Mopar owners, but compared to late-model vehicles the electrical and ignition system of a classic Chrysler product is really quite simple. And while many chose to upgrade their cars with aftermarket ignition systems, or with a Mopar Performance electronic ignition kit, many of us still own and drive cars with a factory points-style distributor as well. One of the questions we're often asked about Mopar ignition systems is whether or not the ballast resistor is a necessary item. In fact, there seems to be a lot of mystery surrounding this part, so this month we'll tell you what the ballast resistor is, why cars have them, and whether or not you need one.

All cars produced with breaker-points type ignition generally had a resistor of some sort in their ignition system. Some brands utilized a resistor in the coil or a resistor wire hidden in the wiring from the ignition switch, but Mopar put their resistor (or ballast resistor) on the firewall or inner fender, causing some to misidentify it as a part of the charging system. In simple terms, the ballast resistor in a Mopar limits the amperage, or current flow, through the coil while the engine is running, thereby extending the life of the coil and breaker points of the distributor. When the ignition key is in the start position, full current is applied to the coil and increases voltage to the spark plugs.

In their electronic ignition systems Chrysler utilized a dual ballast resistor, again to extend coil life and provide a constant primary current, with the system also bypassing the resistor to apply full amperage to the coil during startup. In either type of ignition system, points or electronic, the ballast resistor can be removed to increase secondary voltage to the spark plugs, but the long-term effects of removing the resistor differ between the two systems.

An ignition system with breaker points will surely suffer from reduced point life if the ballast resistor is removed, as higher amperage can damage the surface of the points causing failure. Additionally, if the ignition is left in the run position and the points happen to be open-or worse, barely open-electrical arcs can cause raised spots on the points resulting in a change in dwell timing or an engine that won't run at all.