Well lets start with that it is the 91 in my sig, what it does right now is when you hit the back tank switch the fuel guage goes up to full but the truck then starts to run out of fuel because its not getting any fuel....so any tips what to check first look for or what it is?
thanks
Jared F

 

id say its the vavle. obviously the truck want to go to the second tank but the valve isnt letting it.

but my truck is a single tank so im no expert

 

The valve should be in the tank and is operated by the in-tank pump. Sounds like the rear pump is not running, either due to a wiring issue or the pump has failed.