satyr, remove all the bulbs and inspect the contact points for flat spots which develop with older bulbs, even though the bulbs are not burned out. Replace all bulbs with flat spots and see if that resolves your "Lamp Defective" warning.

Also, inspect for melted plastic where the bulb holders screw into the rear light assembly. On our 1998 E320 the plastic melted slightly and formed a small bulge that prevented the bulb holder from making good contact with the metal portion of the housing. That was causing an intermittent "Lamp Defective" warning. I filed the plastic bulge smooth and that resolved the problem.

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Fred Hoelzle