Welcome to the seadoo forum Phil. If you try and search almost any problem under my name, you will find an answer for almost any repairs.
Here is some information on the guage;
You need to check the Pink and Pink/Black wire coming out of the baffle tube in the gas tank. The sending unit works off resistance. Pull the plug apart at the tank, and use an ohm meter to check for resistance between the two pink wires. The resistance will be different depending on how much fuel is in the fuel tank. If you get no resistance, remove the clamps off the sender, and pull the sending unit out of the fuel tank. Check the magnets on the float in the sending unit. To get to the float out, pop the bottom off and look for the 4 magnets on the float. If they are missing use a strong magnet to get them out of the tank bottom. If they are dirty clean them and re-insert it back in the baffle tube and check the wires again to check for readings of resistance depending on where the float is in the baffle tube. Check the float to see if it “floats” in a cup of gas. Sometimes the float becomes saturated and won’t float in gas…but it will in water, so use gas to check it. If still no reading of resistance replace the sender. If you get readings, check continuity of wiring to gauge. At the baffle you could un plug the guage and using a jumper wire between the 2 wires in the plug on the guage side. Attach the lanyard to power up the gauges. If the guage goes to full the guage is good. If it still doesn’t respond, do a continuity test of the wires to the guage. If all wiring checks out ok, and the guage still doesn’t respond, the gauge is bad.
Do you have a seadoo shop manual? If not here’s an idea for you. You could join as a "premium member". As a premium member you can down load a authentic seadoo manual from the seadoo manual library. In the library is a variety of manuals for almost all years and models. You can view as many as you like on line as a PDF file, or download it and print it for your personal and private use. There are operator manuals and repair manuals for you to do your own repairs on your seadoo. The repair manuals have everything from troubleshooting, repair procedures to winterizing. It contains wire diagrams torque specs and pictures for disassemble and assemble instructions. In the spec sheets it tells everything needed to maintain oil changes, spark plug gaps, carburetor rebuilds and impeller wear ring tolerances. Click on the "Seadoo Manuals" link at the top of the page for more details. If you need any help or get in a jam, we are always here to answer your questions too. Premium members get priority when it comes to getting quick detailed answers.
Keep me posted on your progress.
Karl