Fuel Sending Unit Problem

[MrMilks]

Hey guys, My truck was reading 1/8 of a tank for 3 weeks and its my daily driver so we all know they don't work like that . Any way So I ran it dry and dropped the tank and swapped the sending unit to see if that would solve the problem, well it didn't and I have no idea what the issue could be. I dropped the left tank and only use the right hand tank, could that cause a problem? Also a while back it wasn't sending fuel to the motor so I bypassed the unit that is used to swap between the two tanks and ran a line straight from the right hand tank to the motor and that solved the problem of not sending fuel. Could have bypassing that unit have caused this issue? Any ideas would be extremely helpful.
Thanks for your time.