I have a 2001 e825 that runs great but one annoying thing wrong… the right blinker doesn’t work, which means the right brake light doesn’t work. The bulb is good, the running light works. The left blinker works. If I undo the connector at the back of the light I read about 5v solid when the blinker should be on. It appears I have an older PWB or DC converter (so it appears) and all the wires going in the connector covered in what appears to be RTV. All the harness connections to the back are good.
So the weirder thing is that blinker worked when I bought it but the left didn’t. Now it has switch sides. Since I don’t have a schematic for the PWB it makes troubleshooting a bit more challenging. All other electrical functions work fine. It’s just the left (passenger side) blinker and brake light.
Had similar problem on the right side. I found corrosion and weak connection at the bulb socket. If you are saying that the right turn AND the brake light are not working I would look there. Although they share some of the wiring, the sources are separate. One should not affect the other. You can temporarily switch the right turn wire with the left and see if it works.
Running light is OK… turn signal doesn’t work on front or back which tells me either the signal coming out of, signal stat?, is not happening or there is a partial short to ground.
The reason I say the later is because I found the same issue on a friends car (2 seater) and it turned out to be insulation on the wire had been rubbed thru by the sheet metal of the signal light fixture. You couldn’t see it, and it had the grommet in tact, or so it looked like… but that is what it was. It wasn’t a dead short but low enough resistance that it held off the signal from working on that same side.
I even disconnected both front and back to make sure there were no shorts and no joy.
I do have a nice clean wiring diagram, yes PDF, but it doesn’t show the internals of that PWB… whatever that includes.