Fuel gauge and dual selector
 

I'm new here, just bought an old 82 chevy c20 6.2. Truck runs great. I ran into an issue today and cannot find any real answer on line so hoping someone can help. I noticed today after driving several hours that my fuel gauge had not moved, stuck on 1/4 and selector was on right hand tank. Hit the fuel selector switch and....nothing. went and topped off right tank and gauge remained at 1/4. Checked all fuses and all good. Whats my next move? Thanks for any help