I have a 1991 f150 and the rear tank isnt working. It isnt priming when the switch is turned on so I assume it is the fuel pump. I just bought the truck a few months ago and it hasnt worked since I have owned it to my knowledge. The fuel gauge for the front tank just quit working also. Runs fine off of the front tank, just without a gauge, and the gauge works on the rear tank, just doesnt run. Could these two problems be related, or are they seperate problems altogether? Thanks for the help.

 

More than likely separate problems altogether.
It could be the selector switch on the dash but more than likely a bad fuel pump and a bad sender.
By the way when you turn on the key it does not prime anything. The selected fuel pump runs for one second to re pressurise the fuel lines for starting

 

Thanks for the input subford. You pretty much confirmed my thoughts but I was hoping it could be something a bit more simple and cheap though.