You should check the fuses too.

Interesting.... How could a fuse cause an "always on" condition?

There are two "hot" circuits involved here. The 30 Circuit (12V at all times), and the 15 Circuit (12V with the key ON).

If the 30 Circuit fuse is blown, the radio will only work AFTER the key is turned on, and needs to be shut off manually after the key is switched off. This was the subject of an old service bulletin (approx. 1986). The following models were affected.

126 - Fuse #18
201 - Fuse #19
107 & 124 - Fuse #1

i seem to remember that there is a little two pin plug in the fuse box or relay box that contains a diode to separate the power on things that can be used while key off[such as radio and power seats]this may be your problem.

__________________
David S Poole
European Performance
Dallas, TX
4696880422

"Fortune favors the prepared mind"
1987 Mercedes Benz 420SEL
1988 Mercedes Benz 300TE (With new evaporator)
2000 Mercedes Benz C280
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Ok, got it solved. Here's what happened, strange as this fix sounds, here goes.....

The repair shop said a blown radio fuse (A1) will cause the radio to be always on, and perhaps cause the windows to not work, which is what was happening to me. My A1 fuse was in fact, blown.

I replaced the fuse, and everything worked fine for about 1/2 hour, until it started to do the same thing. I checked the fuse, the fuse was fine.

Went to the repair shop today, he looked at all my "fine" fuses. The metal on the fuses was all chalked up. He said they should be changed; the chalking is preventing a clean connection and it builds up resistance. When resistance is there, it causes heat buildup, which could cause some weird electrical problems, like the radio and power windows not working.

I immediately replaced all the fuses, and the problem went away. All is well now!