Fuel Gauge not working

Hey guys. My fuel gauge hasn't worked since I got my Jeep around a year ago. It's a 1966 CJ6. On a purchase from Walcks, when I was getting a bunch of stuff, I bought a fuel sending unit for it. Before I put the new one in, I decided to put my electrical test light on the old one first, to make sure that it was getting power. It's a test light that has a ground wire with a clamp, and a pointy end that is supposed to poke the wire to test for power, and light up if it does.
Sure enough, it had power, and when the wire was touched, or poked, by the pointy end of the tester, the fuel gauge began to work. As soon as I pulled the tester away from the wire, the fuel gauge didn't work again. I did this a few times, and the same result every time. Would this mean that the sending unit is missing a ground? If so, does anyone have a picture of how the sending unit should be ground?
Thanks for the help!

 

I believe it's the stock tank, but the Jeep has been repainted, and it looks like the tank got painted too. So it might have disturbed the good ground of the tank. I'll try a wire from one of the sending unit screws to a good ground point. Anything I should do in particular to keep it safe, since it's a fuel tank?

 

Never heard of any safety problems but they will leak from rust holes after many years but the smell gives it away.

 

I would disconnect the battery before doing any direct wiring to the fuel tank, just in case it creates a little spark.

 

Ok. Thanks!