Ignition Control Module (ICM) Electrical Feed Connections
Electrical feed to the ICM is through terminal "A" of Connector No. 1 on the module. See Fig 1 .
Terminal "B" of Connector No. 1 is grounded at the engine oil dipstick bracket along with the ECU ground wire and Oxygen (O2) sensor ground.
The tachometer output signal wire of the ICM is connected to Pin No. 1 of the "D1" Diagnostic connector. The wire is routed to the diagnostic connector through a short section of the ECU harness, the engine, and the instrument panel harness. This type of routing eliminates any potential electrical interference from occurring in the various ECU circuitry.
Ignition firing signals from ECU terminal "27" are transmitted through terminal "B" of Connector No. 2 on the ICM. the ignition signal from the ECU is received by the ICM in the form of a 5 volt square wave. As the leading edge of the wave contacts the ignition circuitry in the ICM, the ICM charges the coil primary windings.
When coil saturation occurs, the module circuitry opens the primary windings to collapse the magnetic field in the windings. This induces the coil secondary windings which is then transmitted to the spark plug via the coil wire, distributor cap, and rotor.