I agree about the ground issue. I once had one on my W123 I am having a hard time remembering in detail, but it caused a bunch of weird issues. If I was running the radio, it would turn off briefly when I used the turn signal and also if I ran the cruise control, my tachometer would intermittently stop working. I believe this was because I had replaced my battery cables and the connectors (termination points) I used were not the quality I had expected.

Dkr.