Mercedes-Benz W203 light switch and headlight malfunctions
Why do the W203 parking lights, fog lights and mirror adjustment not work even though the headlights do?
The cause is often the light switch connector: it is oxidised or its conductor pin has broken. Then the light functions and the side mirror adjustments stop working at the same time. Replacing the switch with a new or used one fixes the fault.
What should I do when one W203 headlight does not light and the fuses are intact?
First check headlight fuses 62 and 63 in the engine compartment fuse box. Then swap the left and right bulbs: if the fault moves, the bulb is the cause. If the bulb and wiring are fine, the fault may be in the front SAM, the fuse and relay control unit in the engine compartment.
Why do the W203 lights come on or stay on by themselves?
Moisture in the front SAM can cause odd lighting effects, for example the front lights coming on in a switched-off car. Check that water running from under the bonnet does not get into the fuse box and that the drain under it is not blocked. A broken front SAM can also leave the parking light on after locking.