Dual gas tank/gauge problems

[bravo1616]

I have an 82 GMC K1500 with dual gas tanks. I recently filled the tanks (first time since I own the truck) and it registers at half a tank or less and when I switch to the other tank it doesn't seem to change or sometimes it goes up to full but then goes back to half or less.

Any ideas what the problem is, I was going to start with the selector switch.

[Captkaos]

could be a bad transfer switch, wiring , gauge or the sending unit.
There is a post on how to troubleshoot this.