What's my problem?

 

dash, fuel sending unit, short in the signal line, bad ground..............

Your probably going to have to do some research on your own.

Its almost like telling someone "my car doesn't start.......why" There's really a handful of problem that it could be. If you can get to the fuel pump assembly try pulling the connector off for the fuel sender. If you add resistance the needle will change. You could ground the signal wire and see if the tank goes to full or to empty. I've done this once before but i forget which way the needle actually goes. Less resistance i think it will say full, high resistance it will say empty.........I THINK. It could be the other way. I'd try this first, its about the easier of all the testing.

If your tank is low enough on fuel you can also take the sender out and move the float with your hand and measure the ohm's. If all of a sudden its open at one part on the coil you know your sender is bad. If this isn't it i would try checking the resistance of the pin at the dash.

Get yourself a wiring schematic and go to town.