[CSHADES]

The place to start when checking the problem you have, is to disconnect the wire to the tank unit(sender) and ground the wire. If the fuel gauge reads empty when you have the wire grounded the wiring and gauges etc should be fine. The tank unit will need to be replaced. If the gauge still reads over full when the wire is grounded then you have a wiring,valve or switch problem. If the gauge reads ok on the other tank then the gauge and wiring to the switch from the gauge should be ok. It is just a matter of separating the system to narrow down the fault.