Originally Posted by craig_c
It does go empty when I turn the batteries off but straight to full when I turn them on.
Hasn't been touched since the boat was built so I'm thinking a broken wire somewhere.
you would need to check the wiring on your rib, but usually the live feed goes to the gauge, then from the gauge to the sender, then from the sender to earth. It may be worth pulling the wire off the sender that comes from the gauge, see what the gauge does, then touch that wire to earth. If the gauges goes from full to empty, then it's likely to be a sender issue or a short to earth somewhere. Good luck tracing your wiring, most wiring I've seen in ribs and boats in general is horrendous