Electronic Ignition: Operation: Distributor

The reluctor rotating with distributor shaft produces a voltage pulse in magnetic pick-up. This pulse is transmitted through pick-up coil to power switching transistor in ECU and causes transistor to interrupt current flow through coil primary circuit. This break in primary circuit induces high voltage in coil secondary circuit and fires a spark plug. The length of time switching transistor allows current flow (dwell) is determined by electronic circuitry in ECU. Dwell is not adjustable.