LUCAS "Opus" Electronic Ignition: Operation

With ignition off and engine stopped, the distributor timing rotor will normally be positioned so the iron rods of the timing rotor do not align with the iron core of the pick-up module. When ignition turned on, a power transistor in the amplifier unit completes the ignition coil primary winding circuit.

At the same time, a pulsating alternating current is applied by the amplifier unit to the distributor pick-up module primary windings. A small alternating current is produced at the pick-up secondary windings, which at this stage are magnetically balanced.

Voltage at the pick-up module secondary terminals is applied to the amplifier unit, but voltage is insufficient to affect the transistor controlling the ignition coil primary circuit.

As the engine is cranked, the iron rods in the timing core come in alignment with the iron core of the pick-up module. This causes a magnetic unbalancing and voltage increases to maximum as each iron rod passes the pick-up module. The higher voltage is transmitted to the amplifier. The transistor is switched off and the coil's primary winding magnetic field is collapsed. This results in a high voltage surge in the secondary windings, which is transmitted to each spark plug by the distributor rotor.