With key on, put the pink wire to ground. (frame, whatever, just make sure its a GOOD ground.) Apparently other color wires were used. On non-EFI applications, black is the ground, the other is the gauge wire.
With key on, pink wire grounded, the gauge should peg out.
If it stays on empty, you might be having a ground issue, which is fairly common. Find the black wire coming off the top of the tank, pull it, and clean where it contacts the frame or crossmember, then reinstall.
Senders are fairly easy to "fix" (although I can't get mine to 100% factory specs) I just wrote about "fixing" them.
If the gauge isn't moving at all, I'd suspect it's a wiring or sender issue.