I had allot of strange problems with my 91 190e. Turned out to be a faulty fuse block. Inside the fuse block the connections are layered and seperated with plastic all molded together. Water had got in over the years and shorted circuits out. I found a good one on ebay. Not an easy job, half the fuse block goes through the fire wall.

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2009 CLS550 55,000
2004 ML350 144,000
2004 X5 95,000
2002 X5 165,000
1996 320S 155,000 (sold)
1991 190E 192,000 (sold)
1989 300SE 160,00 (sold)
1984 300D 210,000 owned since 85, (sold)
1984 300SD 160,000 (sold)