The distributor handles several jobs. Its primary job is the distribution of high voltage from the coil to the correct cylinder. The ignition module is located inside the distributor module (as all GM modules are) of the Defender and is accessed by removing the distributor cap.

The ignition module receives a signal from a magnetic pickup or Hall effect sensor in the distributor. The module uses this signal to open and close the ground circuit to the ignition coil to fire the spark plugs. Spark timing is so critical to an engine's performance that most cars, including the NAS 93 Defender 110, use a sensor that tells the engine control unit (ECU) the exact position of the pistons. The engine computer then controls a transistor that opens and closes the current to the coil. Generally, if the GM module inside your Defender distributor goes bad, it usually goes completely dead. The engine won't run because there's no trigger voltage to the ignition coil.

That said, occasionally a loose distributor cap can lead to built up corrosion reaching the ignition module and coil. In this case, opening the distributor cap and spraying the ignition module with WD40 may very well fix the problem. It is recommended to replace the distributor and rotors at tune up.