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 ?

I believe it splits in the back of the car, find where it splits and that may be the prob.....also check the solder points on the socket itself....there's not much that can break there.....it has to be one or the other....neither of mine work at all, its switch related....

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)