Today, my brother-in-law Mike (who has an E30 coupe), and I tried to figure out what's wrong with the power antenna on my E30, which doesn't rise and gets NO signal. Figured out that the damned thing was unplugged! Plugged it in, it rose the height of the outermost section of the antenna mast and stopped, at which point I immediately got signal. As we began celebrating our partial victory, I moved the wiring, and it lost signal. We figured out that an old vampire tap, installed for some reason apparently related to the BMW CD changer formerly mounted in the trunk, was intermittently killing the signal. We soldered the wire back together, and I now have relatively decent signal, considering the antenna only goes up about 1/5 as far as it's supposed to.
We also pulled the antenna motor out and tried to figure out why it doesn't go up any further than it does. I have no idea. I pulled the cover off of mine and off of Mike's spare, and other than some oxidation on the outside of my motor, didn't find any difference. I would have just swapped his in, but his spare didn't have a mast, and I couldn't figure out how to get mine out, so it doesn't do me much good.
Anyway, for now, I have a semi-working antenna with decent enough signal. We'll see if my wife is able to get the news and traffic station she wants on her commute, then move forward with further plans, which will be:
a. Get a new antenna mast, install it in my or Mikes motor, put it back in the car, buy a replacement grommet for the base.
b. Get a fixed antenna, install it, remove the power motor (weight reduction!) call it a day.
c. Plug the hole where the antenna was, get a shark-fin antenna, install it on the trunk lid.
d. Kick it old school, go with the stick-on strip antenna across the top of the windshield!