So I replaced the second gas tank on my 1990 f150 4x4 dual tank truck and put a little gas in it and idled the truck and switched tanks and the engine dies seconds after I switch it over. I thought it didn't have enough gas so I took it to town and filled it up but it still dies on me. However I noticed the gauge goes all the way down even though I just put 18-19 gallons of fuel into it. Could it be a sensor? I've heard it could be the fuel tank selector. In any case I'm new to the whole truck thing and not sure what to do.