Thanks for your response. I took the photos to the dealer. The guys in the parts department had no idea, and the mechanic looked at it but couldn't give me a for sure answer. They even had the VIN. He said it looks like it may be the fuel pump relay missing in photo #1, but that is a different pin configuration than I have seen on a fuel pump relay. It has 4 large pins, 2 at either end, and 15 smaller pins between them (plus 3 empty spaces). The mechanic said the other sockets were most likely for a cruise control/climate control module.
Even if I could just get the name of the part that is supposed to go there, or even a part number from the same part on someone's w126, then I would have a place to start with the dealer. Thanks.

__________________
86 190E 2.3 8v 325,000kms (~203,000MI)
86 560SEL 347,000kms (~217,000MI)
88 560SEL 315,000kms (~197,000MI)
89 190E 2.6 175,000kms (~109,000MI)
90 300SEL 360,000kms (~225,000MI)
91 300E 187,000kms (~117,000MI)