fuel gauge and fuel tank problems

[Prerunner1982]

some of you may know that i am taking a 12hr road trip on sat. i had planned on running a crossover fuel filler neck to the driver side. well i attempted to gather everything i may need to day, i looked at dropping the tank to clean out the grudge and crap since i havent used the tank since my wreck a year or two ago. I decided to check and make sure how much fuel was in there and realized that it wouldnt switch over to that side. i guess after not being used for 2 years it will go bad. I am not going to ask how to fix this here, i will do a search or Brandon can IM/email me and help me out. what i would like to as and i am sure i have asked before and i know a few others have, but i am gonna ask again. my guage reads 3/8ths of a tank as full, when i unplugged the connection to the valve for the tanks the guage read true full. Is this just a default type thing or what? if i remember correctly (though my user text will probably prevail ) a bad ground would make the guage read past full. Is the sending unit bad as it is only reading the driver side tank due to the fact i cant switch it over to the PS and check it that way. Could the bad valve have something to do with it, the guage has been like this for a while and i dont know how long the valve has been bad though i know it worked when could actually fill the PS tank. thanks for any help.