...I'am getting the feeling that the Ground is bad! Did you ground your test light to the chassis? OR the ground 'IN' the socket?? If you grounded in the socket; then try it to the chassis. The back-up light 'Ground wire' grounds at two different studs at the rear tail bulkhesd, at least on the '74, they do...
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.