Ignition Control Module
Electrical feed to ignition control module, only occurs with ignition in the "START" and "RUN" positions. The ECU sends a 5-volt square wave signal to the ICM. Depending on the signal received from the ECU, the ignition control module will advance or retard the ignition timing according to engine load. When the leading edge of this signal contacts the ICM ignition circuitry, the ICM charges the coil primary windings.
When coil saturation is complete, the ICM opens the primary windings to collapse the magnetic field and induce a high voltage rise in the secondary windings. This voltage is passed through the coil wire, distributor cap and rotor to the spark plugs.