Thanks for the excellent link.
Apparently the module I originally mentioned will not work with most Mercedes.
I was told that on most domestic cars when the power window switch is hit that the current to the window motor is supplied. A permanent ground is in place in this type of circuit.
With the Mercedes and some other Euro cars the switch completes the ground circuit for the motor.
'85 380 SL (sold)
'85 Carrera Flatnose
'71 280 SL Signal Red/Cognac