Ok - I'm confused so I have to turn to the experts.

One of my '92 300D's has a tail light issue on the passenger side. All lights work except for the one rear tail light.

I checked the voltage and got the expected 12V on the sockets that are working but got 5V-8V on the socket that isn't working.

I then tried to swap the entire tail light assemble with my other 300D and same issue - and same 5V-8V reading.

I also created my own ground to the car thinking the ground was bad - same results.

Help! I'm out of ideas.

-John

Every exterior light on the car runs through the lamp monitor relay in the back end of the fuse box. Each bulb has its own channel in the monitor relay.

Remove the 6 screws around the frame of the fuse box and lift off the cover. There is a huge black relay running down the center of the relays, that is the monitor relay. Under the relay there are 3 connectors. X1 is 16 pin, X2 is 10 pin and X3 is 8 pin.

Passenger tail light gets its power from F3 fuse. It goes into X1:6 on the monitor relay and then out to the socket on monitor relay X2:10. Both wires on the monitor relay socket are gray/red.

If you jump those two pins on the monitor relay socket the bulb should turn on. If it does then the problem is in the monitor relay. If not the problem is in the vehicle wiring.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech