1986 silverado dual fuel tank system

[kanicsar]

so i am going to replace both my tanks and sending units and the fuel tank selector valve "which i have no choice but to use a universal one" i cant find a true aftermarket replacement. i am being told that i have to install a after market switch does anyone know if i can just use the factory installed switch?

and i am having trouble with my fuel gauge its all over the place either on empty or pegged past full. if you tap on the gauge bezzel the gauge will i assume read the actual fuel level. i have tried to taking the cluster out of the dash and cleaning and tighting the connections but there is no change.

any ideas thank for all your help!!!!