So...it seems that a link adapter - typical pigtail coupler like those often used on trailer wiring harnesses - is needed to make the 1994 window motors work with 1990 wiring.

Does anyone have any clue what the proper name for this gadget is, and where I might find it? Help?

 

You can't just splice the wires from one connector to the other?

 

From what I understand, no. An adapter is needed - think 6 pin round to 4 pin straight type situation.