I assume that your car has an Over Voltage Protection relay. If it does, i would start by replacing it with a new one. If that does not fix the problem, try disconnecting the small wire that feeds the alternator light. The last time i faced this problem the diode bridge in the alternator had burned over and did not stop charging when the ignition switch was turned off, it was bleeding +12 volts through the small wire. If you need more info feel free to PM me.

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600SEL '91
300E 4Matic '88
240D '83
280SE '77
350SE '73
The most complex systems can fail in the simplest way.
Contra verbosus noli contendere verbis, sermo datur cunctis, animi sapientia paucis.

i don't believe in the lord! He's never bought me a Mercedes Benz.