try the trunk light. the pin switch may fail leaving the light on all the time.

I've seen it happen before. not sure how common it is though.

Otherwise I would investigate obvious things first, like the antenna steve mentioned.

ALon

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'92 300CE - Sold
2004 C240 - 744 - C7 Wheels - Android Radio
2002 C320 - 816 - Sport Wagon - Sold
2006 E350 Wagon - 368 - Dead
2015 GL350 Bluetec - 197U