I have a '95 E320. My dash light that indicates an exterior lamp failure came on yesterday while driving. As soon as I could, I checked through all the lights. All lights functions normally. I checked the fuese, and they are all OK. But an interesting thing was found. The right rear bulb assembly unit lacked the base contact for the fog lamp bulb. It doesn't appear to be broken, it looks like it was never there. No bulb, no contact. The left rear assembly was complete and intact (the left rear fog lamp functions normally). The indicator light comes on when I: (1) shift into drive or reverse (I have to press the brake to get out of Park), or (2) without shifting out of Park, I can depress the brake and activate the turn signal (left or right). I have two questions. First, is there an indicator detection unit that could have failed? Second, why did it not come on before when the fog lamp socket was faulty? Thanks in advance for any hints you can give me.