It's either the float or the f1 fuse. Google Seadoo f1 fuse repair seadooforum. This is the worst car scenario. Best case is it's the float and they're around $20. The f1 should have instructions on how to test of the fuse is bad. Hardest part is probably removing the fuel baffle com the tank.
1st, confirm the gauge is working but there is a common fuel baffle fuse issue. The baffle must come out of the tank for repair in that case. Also the hollow float can be full of fuel and sink, also requires removing the baffle.