Have you done the troubleshooting and shorted out the wire at the sending unit? The only thing to do from there is get behind the dash and start checking for an open circuit in the wiring and whether or not you have the correct voltages or ground and if all that checks out ok...it's the gauge.
I'm guessing it will be the gauge if all your other gauges are working.
![Big Thumb Up :biggthumpup:](https://board.marlincrawler.com/Smileys/marlin/biggthumpup.gif)