I have a 1983 F-150 super cab with dual tanks. I know the valves are different because of the Fuel injection on 1985 + trucks. Well, anyways, my truck was sitting for about 5 years on the previous owner's house unused and I bought it a couple of months ago for $85. It was PRETTY BAD cosmetically, but you know those Ford 302 HO V8 don't die easily, so whatever I fixed it up good. I though the fuel selector was dead. First the rear tank was missing, second the fuel selector did nothing when switched, and third, it was sitting on the truck's chassis unplugged and also had all lines removed. It looked very inoperable.

I looked for the fuel selector fuse, noticed it did not have a fuse plugged, so I plugged the fuse and noticed quickly that a "thump" sound came from the selector (fuse is number 3 on the fuse diagram). When I moved the switch from rear to front it seemed to switch. The selector was full of dirt and was stuck on the inside (it didn't seal properly, leaked on both inputs at the same time). All I did was fill it up with WD40 lubricant, switch it back and foward so it became unstuck, strike it softly on the outside a couple of times so the dirt got unstuck in the inside, and blew it on both side real nice with a compressed air gun.

I also added some machine oil on the inside so the rings became unstuck even better with use. I tested it for seal leaks, when a tank is selected, it only gets fuel from the selected input, not the 2 of em' at the same time which I think is important. I made a home made 18 gallon flat fuel tank, got some new fuel lines, clear view fuel filter, and a jeep fuel sending unit. When I got everything put together, well, it works like a charm. You can get a generic fuel sending unit at your local autoparts. I got a Jeep's one.

If your rear tank is missing, the sending unit cables for the fuel gauge should be right on top of the rear axle with a round plastic plug with 2 holes. You can cut off this plug and replace it with some generic spade or round terminals for the new unit. Also, remember to check if the selector switches the sending unit's input and if it works properly. You can do this by conecting both cables together, this means zero resistance (0 ohms) and your gauge should read FULL, or even a little bit over full mark. Hope this helps!