I have a 1980 240d that has only one back up light working (drivers side works) . I replaced the bulb with no luck, then placed the new bulb in the working light socket and it worked. The connectors as well as the socket in the light fixture are in great shape and show no signs of corrosion. Using a 12 volt test light I tested the wiring that enters the light socket and then was no power. I am not sure were to go to continue my search, does the wiring split off at the sending switch and move back or does it split in the back of the car ?