Heat and moisture can both can cause electrical connections to short or open. Unfortunately with jet skis we have to deal with both. Your ski is 13 years old so now you can add corrosion to the problem. You need to thoroughly check all connections and wiring associated with your gauges for corrosion and loose connections. Hopefully it will be something obvious. If not, there is a lot of info on the web for tracking down electrical problems and checking wires for corrosion.