Becker Mexico Sound System Inquiry--how to test

I have a 70's vintage Becker Mexico AM-FM-cassette unit that I'd like to bench test. It has a "loudspeaker" module connected by a multi-pin plug. The back of the main unit has an antenna jack and another smaller multi-pin jack, with 8 positions.

One black wire leads from a small box on the back. Another multi-pin jack appears, with five positions arrayed around a center position; it is covered with a polyethylene cap containing a jumper that connects two pins.

Damn-! This ain't no Delco!! I need help.

The label on the unit reads:

"Mexico Cassette Vollstereo 485 Gerat Nr. 2002151"

Thanks, Danke, Buzzy

PS----I no longer have the old Mercedes from which this radio was pulled. I'm contemplating placing it in an old Volkswagen dash.