Ford Repair: E-350 fuel tank problem, diapragm, tank problem

Question
I have a '89 E-350 with 2 fuel tanks.  I ran the front out of gas(which I had done before), filled it up again and now, I can't get fuel from the same tank.  From what I could see, there is only 1 fuel pump but, just before the fuel pump, there is a "black diapragm" looking "thing" which the fuel lines from both tanks seem to be hosed to; the one tank delivers fuel but not the front tank.  Any suggestions?  I'm pretty mechanically inclined but I hate automotive work.  Thank You.

Answer
Hello and thanks for the question...I'll try to help.
 Your vehicle has three fuel pumps, one in each tank (low pressure) and the one that is mounted on the frame (high pressure). There are two things that can be causing this problem. One is the fuel selector switch, the other is the pump in the tank. My suggestion is that you check the fuel pump in the tank. Use this link for a wiring diagram:

http://www.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/0...

Hope this helps,
Erik