Selector Valve

I gotta 91 F-150, 5.0, 5-speed, with dual tank and 150K. Where is the selector valve the tanks use to switch between. I can't find it on the frame rail. Is it close to the tanks? between? by the firewall? I heard there was a recall on those but the dealer said i missed it. I think its dumping fuel from my rear tank back into my front tank. I know the problem is not my selector switch. Has anyone heard of this? Is it easy to change? Is it cheap? WHERE IS IT? Chilton's or Haynes manuals for my truck do not list it. I can only use my front tank.
THANKS FOR ANY ASSISTANCE RENDERED

anyone?

anyone?

??????????

one last time..... anyone?

wish I could help you - I am having a similar problem....

Drivers side frame rail a bit forward of the front tank, at least thats where it is on the '89 we have here. Just follow the fuel lines coming off of the tank, they will meet at the selector valve.

Thats where mine was on my "87 too