What is this box w/knob? ('95 W124 E320)
 

What is this box w/knob in the lower dash of my 1995 E320 Wagon? And what can/do I do with it?

Thanks in advance.
S.

If behind battery box AND IIRC it is the fuel pump module. Rotating the knob locks/unlocks it for removal. Any part numbers on it?

MAS Relay.

Its a relay for the Fuel pump, A/C compressor and the Air Pump

Sorry for the orientation. Photo should be turned clockwise right 45 degrees so the bracket is upward, then to the right is the steering column.
No pt. # that i can discern (without pulling the whole thing out). The knob looks like it is designed to be turned closer to "I" or "O". What sort of relay is turned? If its the relay, curious that Mercedes buried in this relatively inaccessible nook.

the knob on top is used to mount the relay to the plug.

turn the knob cw to mount and ccw to remove

That is the diagnostic module N59.