GM HEI Ignition Distributor Wiring Diagrams and Guide
GM’s high energy ignition (HEI) distributor has been used as an affordable, easy to install performance distributor since its introduction in the mid 70s. It should come as no surprise being one of the most popular options among modern rodders and race enthusiasts to this day. Most of the original GM V-6 and V-8 models used an ignition coil inside the distributor cap, making it a one-piece ready-to-run distributor. HEI ignition systems are very dependable and offer great performance on a number of applications. The heart of any ignition system is the coil, battery voltage is supplied on the positive side, while the negative side is repeatedly pulsed to ground. When the negative lead is grounded, the primary (low-voltage) circuit is completed and a magnetic field is generated by the coil windings. When the circuit is opened, the magnetic field collapses and induces a high-voltage spark from the secondary winding to the spark plug.
On a factory HEI, the primary coil leads will either be white and red, or yellow and red. The colors of the leads determine the direction the coil is wound, which determines its polarity. Whenever you are replacing a coil or distributor, it's always a good idea to be sure to the ground clip is transferred from the old cap to the new. Without proper grounding, you can damage the coil.
-If you are not using a vacuum advance, we recommend using our lock plate, part number 91012339. This will keep the timing steady without any flutter that the vacuum advance can cause.
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MSD 8225 HEI High Performance Direct Replacement CoilView$109.95Compare