1978 Chevy Silverado - Dual Tank Switch

[cod9939]

Hello,
My nephew just bought a 1978 Chevy Silverado truck with dual gas tanks. The in dash switch to select which tank to use is disconnected. The switch has a short 'wiring harness' physically connected to it approximately 18 inches long and a plug on the end of the wiring harness. That plug is not connected to anything and I looked behind the dash and cannot find where this plug for the switch should be connected? Does anyone have suggestions on where the switch should be connected??

Also, the fuel gauge is not working, the needle is pegged all they way to the right and does not move. Is this related to the gas tank switch being disconnected, or is the fuel gauge a seperate problem?

Thanks!!! Charles