Passenger brake light doesn't work on my 175 (as in it's recently stopped working). The bulb is fine, and when I put a multimeter on the pin I get 0.68v. The ground is shared with the other lights, which work fine, so it's not that. I'm assuming a break in the cable - but I don't know the routing of the cable to check. I'm probably just going to connect it inline with the drivers side one though, as that's much much easier...
Check the main connector that goes into the back of the light unit, they can suffer corrosion on the contacts. I had this issue on the drivers side on my R26, cleaning the connector solved the problem.
I've had that problem with a fog light, but I'm checking the voltages at the plug (where it connects to the light housing). EDIT - Or do you mean some kind of light switch ECU thing?
Turns out I was tracing the wrong bulb, which is why there was no voltage. And the (dual filament) bulb was broken, but when I put a replacement in I put it in the wrong way and it didn't work. I'm normally good with this stuff but apparently had an off day!
