The alternator is case grounded, and does not normally require a separate external ground wire.
The voltage regulator case needs to be grounded.
As JFB asked, is there voltage at the regulator's "I" terminal when the key is in the run position, and is the "GEN" light in the tach on?
With the key off, only the "A" terminal will have 12VDC.
John
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.