I just got my '71 F350 running. It has what I beleive are dual tanks: one behind the seat and one under the bed, on the front driver's side. There is a manual selector switch on the floor by the driver's door. It is marked "Main", "Off" and "Aux".

Which tank is "Main" and which is "Aux"? My fuel gauge is not working yet and I don't want to run the motor out of fuel to learn which is which.

Thanks,

Bruce

 

I'd think your main tank would be the one behind the seat because that's where they were puttimg them anyway.

 

I bought a 73 new with dual tanks. Both mine were under the bed. The valve was labled "main" and "AUX" and the rear was the main. The switch in the Dash was labeled that way too.
I remembered it that way by all the rear main seal's I replaced while working for my dad.
That was sure a clumsey system compared to my 88.
I always had in mind to put a third tank in behind the seat and use the third port on the selector for that tank.
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For your year truck the main tank was the one in the cab. That's how trucks came standard when only one tank was installed. Therefore, the auxilary tank is the rear tank. Since the hoses can be hooked up differently to the valve it's impossible for use to tell you exactly how your truck is configured. I would recommend you follow the hoses and you should be able to determine which is which. The guage should be easy to figure once you know which tank is which. I hope this helps.

Stock Man
1967 Galaxie 500 Convertible (HELP!---I need 15 x5 factory rims)
1967 F-250 FE 390 4wd
1966 F-250 I6 240 2wd LWB Flare Side
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On cool thing about the manual selector valve is that the "OFF" posistion makes for a great security device. If you ever have it parked in a "threatening" place such as a down-town movie theatre at night, switch the valve to the "OFF" position. The thief will still be able to drive away, but he will not be able to go very far; maybe a block or two at best. It will confuse the hell out of him especially when the guage shows that there is gas in the tank. It sort of makes-up for the fact that these trucks are so easy to "hot-wire" and steal in the first place.

 

I recently bought a 68'F250 with dual tanks and my main tank is the one behind the seat and the aux is under the bed. My fuel gauge was not working either but I found out that the gauge selector switch wasn't making a complete circuit. I just had to clean the contacts on it and now the guage works.Hope this helps.-Fuzz

 

 

any idea where to buy or have my floor fuel switch reconditioned as I think it is letting air into fuel line so engine dies. thank you

 

I bought a brass 3 position switch advertised as a marine unit when I added the second tank to my '67. They are easy to find on-line from the usual places. I would suggest spending the time to find one that has the indents on the shaft, makes it impossible to miss the port alignment when switching tanks. The third position acts as an "off" position.

 

My valve only has labeled "AUX" and "OFF". I think it is correct that "AUX" is the belly tank, because the truck dies if the valve is in any other position (and that's the only tank that burns gas).
Does anyone know what direction this brass valve should be for the truck to burn gas from the Main tank behind the seat?

 

@KyleWSith, that's not the original valve. it should have 3 positions. Off, Main ( for the tank behind the seat)and AUX for the tank under the bed (driver's side). I bought a new valve from a marine supply store on line.
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