MOTORCRAFT DURA-Spark II Ignition System: Operation: Notes

When ignition switch is on, current is supplied to the coil through a 1.35 ohm primary resistance wire. As distributor shaft rotates, the distributor generates signals causing module to break the primary current and induce secondary voltage in coil. A timing circuit in module turns primary circuit on again to energize coil for next spark cycle. The dwell varies with engine speed and cannot be changed.