Mercedes-Benz W204 tail light connectors and grounding
Mercedes-Benz W204: why does a tail light dim or give a fault message even though the bulbs are fine?
The most common cause is the connector of the tail light ground wire, which heats up because of poor contact and melts. Replacing the bulb does not help. Check the connector and the ground point. The symptom can be flickering, a dim light or a message on the trip computer.
Mercedes-Benz W204: how is a melted tail light connector repaired?
The repair is to renew the connector, the pins and the bulb socket. In addition, it is worth running an extra ground wire between the lamp base and the body, because the ground of the original base is undersized. This way the fault does not return.
Mercedes-Benz W204: what if the tail light connector is fine but the fault remains?
The tail light connectors and holders are not always the cause. The fault can be in the rear electrical control unit (rear SAM), in the cable or in corrosion of the connector. Fault code B164211 means a short circuit to ground in the output, and it can also be caused by an incandescent bulb added alongside an LED turn signal.