I have no idea whats wrong, and I'm not good with electrical stuff anyway. But the power window switches are infamous for simply breaking internally. All the vendors sell reasonably priced replacements that are very close to the originals in appearance but miles better constructed. Try interchanging the window switches & see if the problem moves with a switch.
PANTERA INTERNATIONAL
A DE TOMASO CAR CLUB
Presents the De Tomaso Forums
The On-Line Meeting Place for De Tomaso Owners and Enthusiasts From Around the World
Clicking on the banner will take you to the sponsor's website.