Dennis, you don't have an aftermarket ignition, do you? If you have an MSD electronic ignition, for example, the tach won't work without the special adapter. No big deal, and it isn't expensive, but it doesn't work without it!
Has it always not worked? Or has it recently decided to "rest"?
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.