E450 Passenger side tail light an turn not working backup is

For the lights, have you pulled the lenses to inspect the Bulbs and Sockets? An "ice pick" test light is very helpful on testing like this. Better than a meter.

I got so tired of rear lamp problems that I replaced our original Bargman incandescent lights with Bargman LED versions. They have to be connected to the wiring supplying the originals. This eliminates socket problems as well as bulb problems. Direct replacement otherwise. Same screw holes. I changed screws to stainless just because I could.