Oreo,

It is the long box on the outside under the screwed on fuse box cover. There are 3 connectors on the bottom. With a little patients you can remove the cover of the unit and get to the circuit boards. I resoldered all the solder joints. I've repaired many MB modules by resoldering. As of tonight mine is still fine, but it has gone weeks without malfunctioning.

Goog luck,

TCG
1992 500E
1986 300E
1975 450SL