Ignition System: Operation

A trigger wheel turns with the distributor shaft. As each trigger wheel tooth approaches and passes the pole of the magnetic pick-up coil, the magnetic field created by the permanent magnet concentrates, strengthens and collapses. As the tooth passes the pick-up pole, the magnetic field collapses, This induces a low-voltage alternating current in the windings of the pick-up coil.

This low voltage signal passes to the control module, which makes or breaks the primary ground circuit of the ignition coil, depending upon the polarity of the pick-up coil signal. This induces a high voltage surge in the coil secondary windings that fires the spark plugs. Control module also controls the dwell angle (coil build-up time measured in distributor degrees).