I have a 1985 528e. I am having intermittent power with my radio when I drive over bumps. Has anyone else had this problem?
You can get the ETM here, http://wedophones.com/Manuals/BMW/ , check out the wiring diagrams pertinent to the stereo system, if the power's definitely cutting out vs. just the sound, presumably that would narrow down the possibilities. Check the ground connections. If you have a booster amp, (presumably in the trunk) that would be another avenue to check and confirm for power and ground.
Electrical gremlins are tough. As Marshall suggests check the grounds. It might be easier if are having multiple issues. But just one thing issue is tough. I think when grounds get funky you may see them greenish.