This sounds most likely like a communication issue, because both are out at the same time.

Or simply a bad brake light switch?

Or bad brake light assembly contacts? Read Dspicher's post, very interesting.
https://forums.edmunds.com/discussion/5796/mercedes-benz/r-class/mercedes-benz-r-class-electrical-problems



Does the IcarSoft MB really say "Open or Short" if so.

If it where a true open you'd have 12v at the beginning of the brake light circuit, but 0v at the bulb.

If where a true full short to ground it would read 0v at the source (where the circuit begins) and 0v at the load.

That's all I can think of.

__________________
1998 Ford Escort ZX2 5 speed - 279,000 miles My Daily

1992 Mercedes 300D 2.5 202,000 - Pure junk
2000 Mercedes E320 Black - 136,000 miles - Needs repair

Don't forget to grease the screw and threads on the spring compressor.