First get a maintenance manual.
You'd be very surprized what you can find in there reading away a beer soaked snowy Saturday afternoon. (sorry, I am traveling so I don't have mine handy.)
While my 03 Road King has EFI, the float assembly is probably in the same location (fuel down spout). The manual will tell you how to take it off and you may discover that there is something hanging it up (a part loose or broken). Or it may just be dead.
I like the gage, but always depend on the trip meter.