Exterior Lamp Failure Indicator

Testing operation of exterior lamp failure indicator

N7 - Exterior lamp failure monitoring unit:

1 Exterior lamp failure indicator as of 10/85 in 2nd field




1 Exterior lamp failure indicator up to 09/85 in 1st field





The following functions of the exterior lighting are monitored by the lamp failure monitoring unit in the relay box and, if a lamp fails, indicated by the exterior lamp failure indicator in the instrument cluster lighting up:

Low beam, high beam, fog, parking, tail, licence plate, stop, turn signal, rear fog and reversing light.

If a bulb fails in one of these circuits, the exterior lamp failure indicator signals the fault for as long as this light remains switched on.

The stop light and turn signal light have a fault storage facility; this means that if a bulb in one of these circuits fails, the exterior lamp failure indicator remains on until the key is turned back in the steering lock to "1" or "0".

To detect the fault, start the engine and switch on the turn signal or stop light.

As several lamps are activated when the lighting is switched on, it is necessary to perform a visual check to determine where the fault is located.

Note: The indicator lamp lights up with reduced intensity in key position "2" as a self-check and goes out when the engine is running.

If additional lights, e.g. auxiliary headlamps, additional stop lamps, trailer hitch etc., are retrofitted, the lights must be connected to the fuse (ahead of the lamp failure monitoring unit).

The lights should be connected ahead of the lamp failure monitoring unit otherwise the exterior lamp failure indicator will not operate properly or the lamp failure monitoring unit will be damaged.


Function check of exterior lamp failure indicator on vehicles with trailer hitch

Note: Since 08/86 no additional turn signal indicator lamp is fitted in the instrument cluster on vehicles with the optional trailer hitch.




The combination relay (turn signals with trailer hitch, heated rear screen, wiper motor) N10/2 is switched over to trailer mode by a signal from the trailer detection control unit N28/1. This detects the trailer mode by performing an electrical measurement through the stop lamps of the trailer.

A faulty turn signal bulb at the trailer is indicated by the turn signal indicator lamp flashing more rapidly. At the same time the exterior lamp failure indicator lights up.

1 To simulate trailer operation, connect a 12 V 21 W bulb to terminal 54 (stop light) and to terminal 31 (ground) of the trailer socket.
2 Turn key to position "2" (ignition on).
3 Switch on turn signal lamp. The flashing frequency is faster than normal and the exterior lamp failure indicator lights up.