Well ND.... I have seen a manual change over valve mounted down there before (like when the dealership installs an aftermarket tank).....evidently you never seen one?

The environmental (heat and air) control panel is the same as a heater/vent/a/c panel.....sorry it an aviation term carry over.

To me it a very understandable comparison.....

 

I don't know of a single dealer that installed an aftermarket tank and I doubt any did, because there was no way to warranty them.

Here on the west coast, many aftermarket tanks (including saddle tanks that FoMoCo never offered) were installed by the Fey Bumper Co., who also sold aftermarket step bumpers.

 

Maybe that is how it was back in your parts slinging days, but I do remember for sure because it was on my fathers truck. So I am not just guessing, and it had the lever for the valve right under the dvrs side seat edge.

When the truck was sputtering he would always be trying to get the lever flipped over before the truck died and it always was quite the issue.

All this was on our 1973 F100 and it was back in the 73 or 74, but I know it was a dealership or aftermarket but dealership installed tank cause I was with him when it was put in.....warranty or not.

 

1973 and 1974 has the manual control selector valve. 1975 was the first year for the electric selector valve that mounted on the frame rail.

 

So it was ok to ask a question about the possibility of a manual valve. I knew there could be one, just was not positive of the years.

I was trying to get some troubleshooting ideas started, and now we know the year the manual valve went to a dash switch, and frame mounted elec valve. (75)

Always great to learn something new.

 

Dude,

Buy a new dash and rear tank switch. Avoid buying old parts. During the installation clean the connectors. Give the old truck a break.

Dr Jack

 

Check the wire on the valve for power as someone switches it back and forth.

OR

Wiring diagrams are available at 1973-1979 Ford Truck Wiring Diagrams & Schematics - FORDification.net
That system is on 1979 Page 3.
The switch is C-402 center of the drawing. C-402 at the bottom will show you the pinout of the switch.

Couple of tests that can be done with a simple test light with one person.

Check the switch by seeing if, while plugged in (key to run if I remember), 973 Red has power. If not check fuse 6, lower left on the block. If it does check 674 BRown-White for power when changing position on the switch. (should only have power in one position, it's on/off)

If you have power through the switch then you might have a bad ground on the valve (grounds through the mount to the frame), corroded wire on the valve (single wire), or its bad. If you don't have power through the switch time for a switch.

As for the gauge portion I haven't troubleshot that part before ..... so I will refrain from guessing.

*******
I was looking for a 79 style switch the other day for the wiring upgrade i'm doing on my 73. Neither part is cheap.

I lucked out and found a switch and solenoid on a 79 in the bone yard very cheap - the solenoid was mounted inboard on the frame before the midship tank.

 

While I agree you should troubleshoot and check everything, don't get upset if you can't find the issue.

I just bought a universal deal that is very similar to the Ford valve. It comes as a complete kit with valve, pig tail connector, switch and destructions on how to put it in. I paid $66 for the whole shootin' match. It works great, too.

 

under the cab floor outboard of the frame

 

Who did you get it through and what was the part #? Just looking at all my options.

 

Is this a separate solenoid from the fuel valve selector or is this where the selector should be? I saw what looked like the fuel valve selector on the front of my rear tank. I have not had a chance to get back under the truck to see if mine is located on the frame up closer to the cab and im seeing something else on the rear tank. Just want to make sure I know how many components there are between the switch and ballpark locations providing previous owners have not relocated them. Thanks

 

As you can tell from the discussion between 77&79F250 and NumberDummy , there was a change in how the switches worked and what did what. 73-74 trucks had a manual lever/valve on the inside cab floor between the seat and the door that controlled the valve for fuel flow only and a switch by the heater control that controlled the gauge. the lever went through the floor and the fuel lines came through the frame from both tanks, went through the valve, then back through the frame and fwd to the engine. 75-up went to an electric solenoid where the manual lever/valve was previously located, so that everything was controlled by the switch on the dash. Same place to put the "works" just add an extra wire or two. Now, what you are looking at on the gas tank is probably the fuel gauge wiring and fuel lines

 

On my 1979 F150 4X4 with dual tanks, the solenoid selector valve is mounted on a frame cross member just in front of the rear tank. It is not mounted on the frame rail or just outside the frame rail. My truck is very original and this was not a relocation of the valve by a previous owner (I was 11 years old when my father bought it in 1979).

The solenoid valve has 1 wire and 3 hoses connected to it. Over the years I have had a few problems with it. The wire came unplugged from it, causing the truck to only draw fuel from one tank (I don't remember which tank). The solenoid casing rusted through on me once in our Canadian winter and I had to replace the solenoid valve. When I replace the valve I covered the solenoid casing with a heavy piece of 1 inch hose and fastened it on with zip ties. That valve has now been on the truck for over 25 years.

 

did not know that about the '79s. I wonder when they did start that. seems odd to take a fuel line from the middle of the truck to the back of the truck, then back past the tank to the pump at the front of the truck

 

I am not sure when they started that. I do have a 1976 F150 with the solenoid under the driver's side floor board/outside the frame as several posters have indicated. On the 79, the solenoid is located in a better spot in terms of being protected better from stones. You are right, it did make for interesting routing of the fuel lines. If I remember correctly it is shown in the parts manual illustrations. With a little digging I can find more information.

As you know, old trucks get modified a lot so it can be really hard to figure out what is original after it went through a few owners. I am lucky to have an original owner, unmolested 1979 truck even if it does have 377,000 miles on it!