The system consists of the battery, ignition switch, ignition resistor control unit, coil, dual pick-up distributor with vacuum advance mechanism, dual pick-up start/run relay, spark plugs and the necessary components for the routing of primary and secondary current.
During engine cranking, the dual pick-up start-run relay is energized through the starter solenoid circuit, which allows the start pick-up to adjust the timing for starting purposes only. As soon as the starter solenoid is de-energized, the start-run relay switches the sensing function back to the run pick-up.
The pick-up circuit is used to sense the proper timing for the control unit switch transistor. The reluctor rotating with the distributor shaft produces a voltage pulse in the magnetic pick-up each time a spark plug should be fired. This pulse is transmitted through the pick-up coil to the power switching transistor in the control unit and causes the transistor to interupt the current flow through the primary circuit. This break in the primary circuit induces a high voltage in the secondary coil circuit and fires the appropriate spark plug.
The length of time the switching transistor allows the current to flow in the primary circuit is determined by the electronic circuitry in the control unit. This determines "DWELL".
Dwell is not adjustable and there is no means to change it because changes are not required.