While I wait for engine parts to arrive, I look for constructive work to perform. Since I’ve long known that my dual fuel tanks had been “modified” by the PO, that seems like something that I will eventually want to straighten out.
This RWD LWB ’76 F-150 has two fuel tanks, a longish one located between the front and rear wheels (midship) which is the auxiliary tank and a squarish one located aft of the rear wheels which is the main tank. There is a switch in the climate control panel labeled Main/Aux that is non-functional because the electrically controlled tank switching device it was attached to was removed and some lines were plugged. It has some as yet unknown influence on the fuel gauge.



Here’s what it looks like today looking front to rear and …



… rear to front. There’s gas in both tanks so I have to guess which one is actually supplying fuel at this point.



The Ford Truck Shop Manual for ’76 provides an overall view of the system …



… with labels for various components. We are interested in “T.”



So using the photos above in conjunction with this schematic make it appear that this truck is getting fuel only from the aux midships tank. That is, if my assumptions about the fuel sources (see question marks) are correct. So, please correct me where I am wrong.



I suppose that this remnant is an electrical component of the fuel tank switcher.



Here’s what that remnant looks like from inside the cab.
So the question is what to do about this. 1) I could leave it as is and operate exclusively with the aux (midships) tank. 2) Presumably, I could change the plumbing around and run exclusively from the main (aft of rear wheels) tank. 3) I could fabricate or acquire some sort of manual switch that is activated on the frame or in the cab. 4) I could restore the original electrically controlled setup or get something newer and better, including the dashboard controls that sync with the gas gauge.
What would you do and why?

 

All of the above solutions are feasible. It depends on what you want the end result to be. Personally, I'd go back to the electrically controlled setup, but that's just how I am. A local parts store should be able to provide a manual switching valve, but that is not going to get the gas guage issue solved. If you start driving it, you will appreciate having 2 tanks LOL

 

each fuel tank has its own ground and its own sender, the tank switcher has a solenoid that then mechanically opens or closes off each tank to the carb, when switched to a particular tank the electronic signal for fuel level from that tank is sent to the fuel gauge in the dash

 

I just added the electric dual fuel panel, switch and wiring to my 1975 highboy(eliminated the manual valve system that was there; It was fairly easy once I located all the pieces.

You could get your system working as designed by adding the missing fuel valve switch, Two working fuel tanks are better than one!

Pick up a Duralast FSV4 for about $40 from autozone. It will plumb into your existing fuel lines.
That wire you show in your last pic was the 12V connection to your missing fuel switching valve.
No 12V present means you draw fuel from the normal position(main tank) when you apply 12V (via the dash switch in your heater panel) the valve and fuel gauge switches to the aux tank.
You just need to figure out which wire is 12V on the back of your fuel selector switch at your heating panel.

Hopefully no one has messed with your fuel gauge wires and all you need to do is add the FSV4 and its 12V connection.
Tbruz

 

I have the exact same setup on my 75. Although in my case the rear tank had a rust hole in it. SO no brainer, I removed the rear tank and lines and run exclusively on the front tank(which at this exact moment I can't remember how many gallons, 28 I think). Which is plenty for my trips/travel distance.