Was once told the larger tank is set up as the main tank on these trucks but I doubt it. Probably has to do more with the influence of the ghost of Henry Ford. Apparently he is still pissed off that these trucks came in colors other than black - so it may be a random setup!

 

First -- Merry Christmas to all here at FTE.
My "78" F150 is marked on the switch, Main (lower position) Aux.(upper position) the Main tank is the side (midship) tank and the rear is the Aux.
When I first got the truck , I ran on the rear tank first, when it ran out of gas I switched to the front tank and it took about 5 miles before it finally started picking up enough fuel to run at highway speed. The reason for this is because the switchover valve is located right in front of thr rear tank. When switched over it had to pull fuel from the front tank back to the valve then up to the fuel pump.(stock mechanical fuel pump). If you run the Main (front ) tank dry then switch to the Aux.( rear ) tank the fuel is only a few inches from the valve and there is no lag. ( apparently when running on the rear tank the fuel in the line from the front tank drains back into the front tank). I had this happen twice before I realized I have to run the front (main ) tank first. Hope this helps. Tyqmonn aka Posford aka Nick Sr..

 

The Truth is:

The REAR Tank on those years trucks that did not have an in-cab tank (ie: 1978).... is considered the MAIN Tank.

The side or saddle tank FRONT is considered the Auxilliary Tank

 

I have to disagree with you Mil1ion, in the 78 F150 the front (side ) tank is the MAIN & the rear tank is the AUX. Nothing on my truck has been changed and that's the way it is.

 

the 6 shop manuals and part breakdowns all list the inbetween rear rail tank as the main. ford even calls the saddle tank aux, my build sheet says aux saddle tank. all the trucks that did not have the aux from factory still had the rear tank, so that is the main tank. the saddle was extra. i have the ford truck buyers guide for 73 and 78 it lists a side saddle tank as optional.


the thing is it is really easy to screw the system up. on the selector valve there is 3 hoses one goes to the fuel pump one is main the other is aux. when people replace the hoses they sometimes get put on the wrong port. so you could turn the aux into the main by just flipping the hoses

 

Ty,No offence at all.

You can agrue all you want.

I go by Ford's explanation not hearsay.

The position of the switch means nothing.
It is a physical Attribute. The Main tank goes near the rear axle.
The Side AUX tank is an add-on .

 

Hi, again I believe both of my trucks to be original.On page 9 of the original owners manuel my Lariat came with (brown book 1978 0wners manuel for f100 thru f350 series printed NOV 1977 2nd printing part # d8TA-19A32-BD) It states

The fuel valve is energized when the fuel selector switch is moved from MAIN to AUX position,allowing fuel flow from the auxiliary tank.On vehicles equipped with duel fuel tanks,the ""MAIN"" position supplies fuel to the engine from the midship fuel tank.

It also provides a diagram AUX up Main down for switch

I agree conventional wisdom would say that since all our trucks of that era had at least the rear tank and the front or mid-ship tank was a option that the rear would be considered the main tank.That however is not the case.As stated above by the manuel the rear tank in a dual setup is called the AUX and the mid ship is considered the Main. nuff said and Happy Holidays

 

look at it like this no rear tank no way to secure the spare tire,so it is the main.

 

I edited my previous reply

 

thats the same diagram i have. thanks

 

Hi Milion,Just so I understand you.Are you saying that the owners manuel is wrong.I don't know how you interpet the diagram.I look at it like this way.1st off the rear tank is labeled standard (not main) in the diagram and I think we all agree that that back tank was standard on all our trucks.2nd I think in that particular diagram they use the word auxillary when a better word would of been optional.I also think we agree that the mid ship tank was a factory option.So (with no disrespect) I think because when the diagram was written the powers that be used the word auxillary when they should of used a more appropriate word like optional. Some folks in here think the diagram and the way the engineers set up or labeled the switch or governed how it worked is connected.I don't however.I believe the owners manuel not a misworded diagram.I can scan and email anyone who want's to see what the manuel says(earlier post)Regads to all 78

 

78f250supercab...(and others )

The midship tank refers to the tank between the frame rails in the rear... kinda confusing... the auxilliary is on the side... This is how my 79 is.

 

For what it's worth, On my 77, my cab tank is the main, rear is the auxilary. It could be all goofed up, I don't know. I'm just happy that they both work.

Wouldn't the guage be all messed up if the tanks were plumbed into the selector valve wrong? Just a thought.

 

I guess I'm glad mine just says Front/Rear. No confusion there.

 

On 78 and 79's the rear tank is the main and the side tank is the aux.
Maybe diffrent on 77's and before!