Birdieall,
You have sort of proved that the new gauge is functional. With the key turned on and the sending unit disconnected, the gauge should swing to FULL...yours did! If you take the same wire and ground it to a shiny clean good ground, the gauge should swing to EMPTY...my guess is that it will. I don't know if you are doing this with the wire AT the tank, but if you are (and you should), it is also proving that the wire is good from gauge to tank!
That points the fickle finger of fate at the sending unit. It pretty simple..it's either the gauge, wires or sender, and the above test will pretty much rule out the gauge and wires.
Stuart
