I have a 1972 GMC pickup truck C1500 with a fuel gauge problem.the problem is when I connect one of the two wires to power and the other to ground the needle goes to empty,when remove the ground it goes to full.also when I take the other that was used for ground and connect it to the sending unit the needle goes past full.so anybody please tell what's wrong and how to fix this problem. Thanks

It could be the sending unit is bad

If it reads full with no wires attached, it may be the gauge.
I think on this, 1 terminal gets power from the ignition circuit and the other goes through the sender to ground, I can't find the resistance for full and empty yet.
I would connect the gauge as it was, look for a hot when ignition is switched on, then if you can get to the sender, momentarily touch to ground and have some one tell you if the gauge moved or not, then if no needle movement was your original problem, then replace the sender.
You could check to see if there is any resistance to ground on the tanks sender wire.

The sending unit is brand new and is at 19ohm and the gauge only has two connect points and what should the power be to the gauge.