Sounds like you are refering to the retaining device on a MAS or DM.

As the size of these boxes went from small relay to approaching the size of major controllers, MB evidently got worried about the ability to retain a good solid connection.

The relay is p[laced just so in the socket and then it is pulled the appropriate distance into the connector by the semi rotating screw knob on the top. The two positions I and O are in and out (maybe not in that order) couterclockwise is Out and clockwise is In. To remove the relay just turn the knob.

The MAS is a replacement for the OVP, fuel pump relay and the klima relay. Everything was consolidated when they started needing more such relays. The MAS also does at least the power circuit for the secondary air pump (clutch coil in your case).

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician