Mercedes-Benz W220 tail light, rear fog light and reversing light faults
W220 tail light does not work and changing the bulb does not help, where is the fault?
The tail lights have no fuse of their own, because the electronics of the SAM control unit protect the circuit. The most common cause is oxidation in the bulb socket, the rails or the surface of the lamp. Clean the contact surfaces and connectors with contact spray and dry off any moisture.
Why does the W220 rear fog light not work although the bulb and wires look good?
An oxidised bulb base or holder breaks the contact, and replacing the bulb and wiggling the wire has fixed the fault. The rear fog light is controlled by the SAM under the rear seat cushion. Oxidation in the fuse sockets and a poor ground can also cause the fault.
Why do W220 tail light error messages appear or the indicator ticks rapidly?
The indicator ticks rapidly when the bulb on one side does not work or the ground is poor. Sand the contacts and rails of the bulb sockets clean and check the ground. A new bulb may need to be acknowledged with a diagnostic tool or a few drives.
Can the towbar wiring affect the W220 tail lights?
Yes. Oxidised pins in the trailer socket or a damaged wire can prevent the lights from working and cause a trailer module error message. Check the socket and its wire first. The lights must not be connected from the socket directly to the car's lights.