Lamp Out Indicator: Description and Operation

The exterior lamp failure monitoring unit N7 in the fuse and relay box F1 monitors the function of the bulbs in the following circuits of the exterior lights:
- low beam,
- side light,
- tail light
and
- stop light.

In the case of low beam, side and tail lights, the exterior lamp failure monitoring unit also additionally monitors the function of the fuses.

The condition of the bulbs and fuses is detected by constantly measuring the current. If all the bulbs are in order, a positive signal (12 V) exists at the monitoring unit. In contrast, if a bulb or fuse fails, a negative signal exists.

Failure of a bulb or fuse in the circuit of the low beam, side or tail lights is indicated by the warning lamp A1e14 in the instrument cluster A1 only when the exterior lights are switched on.

Failure of a bulb in the circuit of the stop light is indicated by the warning lamp A1e14 after the service brakes are operated only if the ignition/starter switch S2/1 or the glow/starter switch S2/2 is in position 2, or when driving, only provided the engine is running.

The bulb failure warning lamp A1e14 comes on for about 30 seconds as a self-check from position 2 of the ignition/starter or glow/starter switch. It goes out immediately when the engine is running.

As bulb failure is indicated after individually measuring all the monitored bulbs, a wrongly installed bulb with an insufficient wattage may also be indicated as a failure. A bulb with an excessive wattage is not indicated.

When retrofitting additional lighting equipment such as auxiliary headlamps, auxiliary stop lamps, towing device etc., ensure that these are connected to the fuse upstream of the exterior lamp failure monitoring unit N7. Other types of connections may cause problems with the indication of the warning lamp and result in damage to the monitoring unit.