Checking the functionality of headlights and horn (Mercedes-Benz M-Class W163)

1. Turn on the ignition and check the functionality of all external lighting devices.

2. With the help of an assistant or by backing the car up to a wall, check the functionality of the brake lights. When you press the brake pedal, only the brake lights should light. Turn on all possible lighting devices located in the rear headlights (reversing signals, parking lights, etc.), then press the brake pedal again. If, when turning on the brake lights, you find a malfunction in the operation of any of the other switched on lights, this may be due to an unreliable contact with the "ground" or poor contact in the headlight unit.

3. Now check the functionality of the head optics. Turn on the low beam, then the high beam.

4. If burnt-out lamps are found, replace them following the recommendations given in Chapter On-board electrical equipment.

5. Check the functionality of all interior lighting devices, including the glove compartment and luggage compartment lighting. Turn on the ignition and make sure that all indicator lamps light up. In Chapter Controls and safe operating techniques describes in detail which lamps should light up when the ignition is turned on. Start the engine. The indicator lamps should go out. When driving in the dark, check the functionality of all the backlight lamps (both the instrument cluster and the dashboard). If a malfunction is detected, refer to the corresponding Section of the Chapter On-board electrical equipment.

6. Sometimes, lamps can fail due to rust appearing on them or on the sockets. Replacing the lamp will not solve the problem. In this regard, when replacing any lamp, carefully inspect the socket from the inside. If you find green or white deposits, remove them with sandpaper.

7. Finally, check the functionality of the horn.