I swapped the questionable tach with known good pantera tach from a running car. It worked.
The questionable tach failed to work in the pantera I borrowed the good tach from.
The bad one is going to Jon Haas for repairs.
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.