I'm driving a 1983 W126 (280SEL), and I'm trying to determine if the above part is simply a socket/plug, or a idle control relay, or otherwise.

This small, square plastic unit is located in the middle of the firewall, about one and a half feet to the left of the battery. It measures approximately an inch square, and has this part number inscribed on the black-colored cap: 011 545 5028.

Does anyone have any idea what part is this?

Thanks!

Mervyn