PeachParts Mercedes-Benz Forum - View Single Post - All power does not disconnect when key is turned off

Jeremy5848 · #11 06-19-2008, 01:05 PM

Quote:

Originally Posted by barry123400

All current is not shunted through the key switch electrical contacts on a lot of cars. . There might be a load relay that has stuck or welded contacts. Does anyone remember if these cars have one? The key switch normally turns a cars load relay on and off again if it has one. At this point if there is one in your model it is the best suspect. Does this jog anyones memory?

This is a great thought. According to the FSM, the aux fan does have a relay, which could be sticking on when it gets hot. The switch contacts in the relay come from a fuse that is hot at all times (can't read the fuse #, CD-ROM has insufficient resolution).

Aha! Page 108 of the circuit diagrams in the FSM [attached] shows that the charging light and the brake warning lights are interconnected through the "warning system," a complicated electronic relay that involves the door-open, key-in-ignition, and seat-belt buzzer. The warning system is a little metal box located under the dash and just to the right of the parking brake pedal. I can't find its schematic in the FSM; the index says "next index" and then the next index says "previous index."

If I had to take a guess, I'd replace that warning system thing. I had a problem with the analogous module in my '87 300D-T (W124, OM603) in which all kinds of screwy things were wrong in the dash. Replacing the warning module fixed the problems.

Jeremy