Ignition Coil: Description and Operation

HEI Integral Distributor:

HEI Wiring Diagram:

The ignition coil is located on top of the distributor cap and uses a low primary voltage to create a high secondary voltage to fire the spark plugs.

The coil is a transformer which steps up battery voltage (12 volts) to high voltage (25,000 to 35,000 volts). The primary circuit is energized when the ignition switch is in the "ON" position. When the ignition module breaks the circuit to ground, on the primary (negative side of coil) circuit, the magnetic field collapses, which induces high voltage in the secondary circuit, which finds its ground at the spark plug.