300E lamp warning light
I had this problem with my 300E(1986). I found that the bulb clips on the tailights are often weak and jiggle out of their sockets. The actual light which was out in my case was the right side rear bulb on the side of the taillight lens. It looks ok until you compare it with the left side. Any object pressed against the tail light covers tends to cause the bulb to dislodge. I usually give it a tap and the inside dash warning light extinguishes. Hope that helps.