I just searched with your user name there and found the old thread.
I have searched for you for the plug in the parts catalog, but so far I did not find it.
Edit, checked the plug under the panel of my friends car, it goes into the control unit for the sunshade, BMW Wiring Cable Plug Terminal Connector 4 Pin 1378141, new number 61131378141
AMP 963001-1
plug for switch of sunshade of e31 must be a 6 pin plug. No success so far to find that Steckergehäuse