Switch and wiring are visible in this photo. This AFAIK is best sourced from one of our vendors. I'm assuming that you would have seen it if it was still installed. Mounting is not quite as simple as it might appear for if the switch threaded portion gets installed too far into the selector housing box it can mechanically block the ability to get into reverse.
Larry
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.