My 1969 fuel gauge has stopped working. The needle stays on full and does not move.  The gauge or sending unit bad?  Any suggestions. Thanks

First do a little test. At the fuel tank, there is a brown/tan wire on the sending unit. Take that connector loose, and with the key on, engine off, ground it(use a short piece of wire, or a small screwdriver as a jumper) to the frame. If the fuel gauge goes to "Empty", the wiring, and the gauge itself are good, and your problem is with the sending unit.
 If it does not go to Empty, then you have either a break in the wiring from the sender to the gauge, or there is an issue with the gauge itself.

Correct me if I'm wrong but I think you've got it back to front, if the sensor lead is grounded it will go to full not empty. If it reads full all the time then it's either a short in the sensor lead or in the tank sender unit.
If you disconnect the lead at the sender then switch on the ignition the gauge should drop to empty, if it does its the tank sender if it stays full it could be the gauge or the sensor lead, if you check resistance of the lead to the chassis and it's very low you'll need to get to the back of the gauge and disconnect it there and check again to narrow down where the problem lies.
Graham

With apologies to our sponsors, ,Wilcox has a very good diagnostic procedure on their site!

Thanks I will look at the Wilcox site and try the tests that were mentioned by the other members