Main Lighting System: Notes

The main lighting system is operated by a latching rotary switch located on the fascia. Movement of the switch to the side/parking lamps or headlamps position completes an earth path to the BECM. When the switch is in the side lamp position, the earth path is completed on one of two pins to the BECM.

When the switch is moved to the headlamp position, the earth path is completed on both pins. The BECM interprets the earth path as request for side or headlamps and provides power outputs to the applicable circuits to operate the lamps as requested.

The BECM outputs are driven by Field Effect Transistors (FET). The FET's detect the continuity of the lighting circuits. In the event of a bulb failure or a short or open circuit, the break in continuity in that circuit is sensed by the BECM which then generates a "BULB FAILURE" message in the message center specifying the bulb which has failed.

When an FET detects a break in continuity, the output from the BECM to the affected circuit is deactivated. When the fault is corrected, the lighting switch must be switched off and then on again to reinstate the output. On certain circuits, the output will be reinstated by the BECM automatically.

The number plate lamp circuit is internally linked inside the BECM to the glove box lamp circuit. If a number plate circuit failure occurs, it is advisable to check the glove box circuit at the same time.

To maximize battery voltage during engine cranking, most BECM controlled functions are inhibited. During cranking, only the side lamps will remain on irrespective of lighting systems active at the time of cranking.