well im thinking that this was a button only outfitted in the euro cars.... as in my owners manual it has lights on the dash that light up when i turn the key on but in the manual they say (No Function) its kind of wierd that they have lights on the dash that mean nothing.. I assume it is for things outfitted in the eurpoean cars.

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2001 Mercedes-Benz C320 3.2
1991 Mercedes-Benz 300E 3.0