Mark,
It is the speedo drive wire at the connection on the Tremec. It usually goes intermittiend but sometimes just stops working. I doubt you will be able to visually see anything wrong there but that is the problem. 100% certain. Also, is your odometer working but not the speedo or the whole wack? Most of the time the wire about 4-5 inches from the plug ( probably grey ) on your car is the culprit. There may even be a homemade Saleen splice there wrapped in electrical tape.
The conncetion just above the driveshaft almost on top of the trans on the drivers side.
