If the window motor works on a rear window, but the glass doesn't move, most likely the little plastic slider in the bottom of the window where the regulator attaches is broken off.
You must remove the regulator from the car to fix this, doesn't take long, so if you are not comfortable with it, takes about half an hour at a mechanic.
The mess made of cars at ANY stereo "store" is incredible. the rear vent system on my brother's 75 300D was butchered into, in spite of the fact that there were two very obvious knock-outs for speakers in the rear package shelf.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!