it is the 85 F250 with the 460 card model engine.

I have 1 psi fuel pressure to the carb and the fuel guage does not work and the selector switch seemt to test fine but does not seem to function.

There is power going to the dash switch but none at the selector valve.
The previous owner put a jumper wire to both fuel pump hot wires from under the hood (drivers side fender) to just before the selector valve, and was driving it like that!
If I pull the wire, the newly installed glass see through fuel filter gets some bubbles and then no fuel!
The fuel system fuse is not blown.

As usual the wiring diagram seems simple but where are all those connections located so I can test continuity from one to the other!

Did ford even make a wiring diagram location picture book back then?

The tank selector switch shows 6 wires in the diagram, but it only has 4 on it!
And the wiring diagram shows an EFI inertia switch before the selector switch!

Also, how do I test the motorized selector valve?
It's not even in the book!

There was even an electrical stud mounted on the firewall (I found while chasing wires) between the brake booster and fender with two fusable links attached that had a power wire that was coming through the firewall under the brake booster unpluged!
I tested the fusable links for continuity and they tested fine, so I plugged it in and nothing changed as far as I can see!

Anyone have experience with this system?

 

The diagram I have in my Haynes manual shows 4 wires to the selector switch. It also shows the motorized selector valve. Do you have a Haynes manual?

Put a meter or test light on the pink/black wire going to the selector switch. When you turn the key and crank the motor, do you have voltage on the pink/black wire? If you do have voltage, does the voltage go away after the truck starts, and then the truck will die in a minute or two?

 

Haynes #880 1980 through 1988 ford trucks page 349, 1984 through 1986 page 3 of 7.

Out the top is 787 PK-BK

In the middle shown as separate wires as they go through the connector #C 446 before they connect,
top to bottom is
786 R
786 R
789 BR-W
789 BR-W
Out the bottom is C 446 BK

Perhaps the red is actually one wire coming out through the connector and the same for the brown and white wires?
I will test as you suggest tomorrow and get back ASAP.

 

Well, I kind-of missed that. At least we are on the same page now. The pink/black feeds the switch, so I figured if you have voltage there all the time, then your pump relay, inertia switch, and oil pressure switch are working.

 

I figure its a bad connection between C446 at the selector switch and C125 at the selector valve, which leaves C124 somewhere in between, before the splice, BUT WHERE IS IT LOCATED!

If I cant locate it, I cant test it for continuity going either way!

 

Well, I got a NEW Haynes manual (80 through 96) that has all the onfo I need!
The old one (80 to 88) never mentioned the selector valve or the in tank fuel pumps used with the carb 460!
And even the ford dealer does not have the replacement plug for the selector valve
If I cant fix it without spending $114.00 for the generic replacement harness and valve, I guess I'll bypass the valve just to get it running for now.

 

A wild guess is C-124 is at a spot that seperates the in cab wiring from the frame wiring, so they can drop the cab onto the frame at the factory, and then plug the two harnesses together.

 

OK, the wires at the valve are supposed to be (#1 pos) and (#2 neg) for rear tank, and (#2 pos) and (#1 neg) for the front tank!
This idiot had them both POS!
#4 is the fuel gauge and #3 front and #5 rear tank's switched with the valves!

And the 1psi I get, must be because it's grounding through the pump body and the fuel tank!

I pulled the valve and tested it, the motor goes "snick" and the air goes like it should, then "snick" and it's the other way and the sender wires switch as well!
It works like it should!
$120 saved!

Now I already tested the dash switch and it works when switched and gets power and I now know there is a switched setup for neg and pos so I will now test for ground at the appropriate wire at the dash plug for the switch.

And if it tests OK, it's got to be C 124, the one I wanted to check that first day, but could not friggen find!
I dont see it under the hood, so it must be under the filthy dash!
This truck needs a bath inside and out!

One more step to drivability!

This guy HAD to give this one away!
It would have exceeded the high blue book in labor alone!

 

I am sure your on the right track, although I don't understand your terminology very well. I don't see any negatives in this system except the #57 black coming off the fuel switch(I am curious what this is for), and the #57 black's coming off the fuel pump/sending units in the tanks.

Putting one meter lead to ground, you should get 12 volts on the red wire, or 12 volts on the brown/white wire, depending on where the switch is positioned.

If you want to read voltages without having to crank the truck all the time, you could take the darkblue wire off the starter side of the solenoid, and hook it straight to the battery for testing purposes. It hooks to a fusible link, which then hooks to the pink/black which feeds the selector switch.

 

You said
"If you want to read voltages without having to crank the truck all the time, you could take the dark blue wire off the starter side of the solenoid, and hook it straight to the battery for testing purposes. It hooks to a fusible link, which then hooks to the pink/black which feeds the selector switch."

There is a fusible link that I did not know about and now will check as it could be part of the problem!

I say again, the guy that thought up those fusible links needs to be dragged out back and shot!

The power for the pumps and the valve comes through the dash switch, goes to the pump and through the valve, returning to the dash switch to ground.
When you flip the switch, the pos wire and neg wire switch jobs, the neg becomes pos and the pos becomes the neg, so if the harness gets unplugged at connector #124 and you jump power to any pump power wire down by the valve, it wont work as the ground is also missing!

You need to make one a pos and one a neg for it to work either way.
What is missing in the newer books wiring diagram is C 124 between the dash switch and the valve, and the power wires that go to the in tank pumps between C124 and the valve!

 

I don't know if my old diagram is right, and I was hoping it was the same as yours so we could troubleshoot, but mine shows a ground for the pumps/sending unit at each fuel tank.

It does not show a ground for the motorized switching valve, which I believe is an omission, or a mistake, since like you said, you do need a return path to ground for it to work.

 

Page 4-13 has a diagram that looks like what I have, the 6 port selector valve and what not, but is not the complete "hot Fuel" system at all!

The pumps are grounded through the tank and the valve is grounded through the switch that also supplies the power.

The "hot fuel" system is on page 4-20 in the EFI section, and has an early model, mine, and a later model!

It explains why EVERYTHING tests as functioning properly, the switch, the oil pressure switch, fuel selector valve, inertia switch (missing and wires twisted together) all the wiring has continuity where it should, there is power where it should be, and a ground where it should be, all of it tests OK, except that the pumps dont work!

There is one thing I did not know was there until the wind turned a few pages and I saw the true diagram for my system, and I cant locate or test that one thing!
It's that tank selector relay that selects the pump on a separate circuit from the rest of the system!

By process of elimination, it's either that component or it's plug that must have the problem!

The ford dealer tells me that part is no longer produced, and cant even tell me where the damn thing is located!

If I can find it, I can test the wiring and the component itself!

 

They wont let me correct the prior one, so this it the updated one!

Well, C124 tested OK!
There appears to be nothing wrong with this system, except that it does not work!

Then I learned something!

Page 4-13 has a diagram that looks like what I have, the 6 port selector valve and what not, but is not the complete "hot Fuel" system at all!

The pumps are grounded through the tank and the fuel valve is grounded through the switch that also supplies the power.

The "hot fuel" system is on page 4-20 in the EFI section, not on 4-13, and has an early model, mine, and a later model!

It explains why EVERYTHING tests as functioning properly, the switch, the oil pressure switch, fuel selector valve, inertia switch (missing and wires twisted together) all the wiring has continuity where it should, there is power where it should be, and a ground where it should be, all of it tests OK, except that the pumps dont work!

There are two things I did not know were there until the wind turned a few pages in the manual and I saw the true diagram for my system, and I cant locate or test those two things!
It's the tank selector relay that selects the pump on a separate circuit from the rest of the system and the fuel pump cut off relay before it!

By process of elimination, it's either one of those two components or their plugs, or wires that must have the problem!

The ford dealer tells me that those parts are no longer produced, and cant even tell me where the damn things are located!

If I can find them, I can test the wiring and the components themselves!

Anyone know where they are?

 

If we can assume the diagram I am using is correct(it is for the correct year an does not have efi mixed in with it), the pumps in my diagram are selected by the dash switch. The fuel sending unit signals are switched by the motorized valve selector.

 

Maybe, as there were three systems used for the carburated dual tanks (I'm starting to think I have gone through enough with this problem as to be considered an expert with this system)!

There was the standard system that is on page 4-13 (in the newer Haynes manual), and the two 460 "hot fuel" systems, early like mine, and late, more like the standard system but a few things from the early system included, that are on page 2-20!

The relays were right next to the drivers fender under the cruise control and the trailer relay is also there!

My testing showed that there was no power coming from the oil pressure switch when the engine was running, but the dash shows oil pressure.

I was going to jump the inertia switch power to run it, but that has power all the time and the pump would run the battery dead, so I jumped it from the ignition module right there on the fender.

And it works except for the fuel guage, but I have to put more fuel in it to verify if I need to check further.

I only get 3.5 psi but the volume seems more than adequate to do the job!

I have a spare generic electric pump if the in tank booster pumps need the help, because those suckers are $150.00 each!

I also decided to move the exhaust outside the frame rail and mount a spare VW van fuel tank inside the frame opposite the main tank as a fuel transfer tank.