dual tank wiring diagram 1990 F150
 

My 1990 F150 4X4 won't run when the rear fuel tank is selected - tank is full, gauge properly reads full, engine dies immediately, quickly restarts when front tank is selected.

Does anyone know of any web source where I can download a wiring diagram of this portion (dual tanks, in-tank fuel pumps, selector switch, relays) of the electrical wiring system for this truck?

You can buy a diagram at www.helminc.com.

Sounds like you need to pull the bed and replace the rear FDM (Fuel Delivery Module).
Here is the diagram you wanted:
http://i54.photobucket.com/albums/g91/subford/Fuel/Fuel-sel1990F150.jpg

Thank you for the link - it's exactly what I was looking for, looks like great fun to troubleshoot this thing. I have two carbureted '85 and and '86 E350 vans, and I've already done the drop-the-tank thing with them to replace fuel pumps. Maybe this time I'll get lucky and it'll be something simple, but it never is! Appreciate the lead, thanx.

nope only goes back as far as 1995 ford f150

I bet back in 2006 when this thread was created it was available. If helm doesn't have what you want, you can probably get what you want on ebay. What do you need? Some certain specific circuit on a certain model, certain year?