There is obviously power getting to the 'up' side of the motor, so either a) the upper limit switch is bad and/or triggering early or b) something is mechanically stopping the lights going further. The headlight motor has the same plastic gear as the windows and can crack leading to this symptom where it will go so far and stop.
Firstly I would jump a battery to the motor terminals and check for up and down travel (checking both limit switches are not contacted). If you have full travel it's a wiring issue and you can work backward from there. All the wiring diagram are available at Pantera Place;
www.panteraplace.com/page107.htm
Julian
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.