Probably about two years ago the stereo in my 240D crapped out. It would work intermittently but mostly just not at all.
The internet and history led me to believe it was a bad ground. That tested okay. Then I redid and soldered all the connections in the hopes that issue was just in crappily done connections.
Didn’t think it came out too bad for my first time attempting this. I didn’t even burn myself(that much).
Tested it out..... Aaaaannnnnnnndddddd nothing.
Then I began pulling each set of speaker wires one at a time with the ignition on. When I pulled the right rear speaker the other 3 turned on. “Huh?”I removed that speaker, and using a short piece of speaker wire, hooked it to the stereo. It worked! So I ran new wire to that speaker and everything works great now. Apparently one speaker can disable an entire system.