It's kind of confusing when people are referring to 'front' and 'rear' tanks when there are !!!!!THREE!!!! possible locations for the fuel tanks. Depending on the year there was the in cab, mid-ship (in front of rear wheel), and back of bed (behind rear wheel).

Million, the picture you posted was from a 73-76 owner's manual. That photo is correct for those years. I've owned two '76's. The main tank was either in-cab or back of bed, depending on how equipped. The mid-ship tank on both was the aux. In 76, the regular and crew cabs had in cab main tanks. The supercabs had back of bed main tanks.

Around 1977, the in cab tank was deleted, bed doors were installed and the standard tank was the back of bed location. The optional tank was still mid-ship. However it seems that in 78 and/or 79 the mid-ship tank got the 'main' designation. Not sure why.

 

Trying not to confuse people here, but this is how the tanks were on all the Fords I've owned or on my father's trucks...

On my old 1972 the cab tank was the main, the saddle tank was the aux.

On the 1973 the saddle tank was the aux, and the rear tank was the main

On my father's 1976 it is the same as the 1973.....


On my 1981 however.... (I know not much relevance cause 1973 to 1979 etc) the saddle tank is the main and the rear tank is the auxillery. Say's so in the manual.

How many licks does it take to get to the center of a tootsie pop? The world may never know.

MERRY CHRISTMAS!

 

I'll be checking borchures later today to see if the pics of the interior show the wording for the fuel switch.

From what I have heard , The dash fuel switch can be installed either way up.
I don't believe that ,I have to go look at one.

Perhaps the problems exists at the under body fuel tank seperator switch ?

Harness tampering

 

I've read and re-read this thread to the point of getting bleary-eyed. Wanted to add my $.02's worth to the subject.

Here's the way my 1976 F-350 140-inch WB Super Camper Special is wired and plumbed regarding the dual tanks (there is no IN-CAB tank in my 76 SCS).
As they say, "Your mileage may vary...."

BTW, I have confirmed the wiring conforms to the FACTORY ELECTRICAL SYSTEMS SCHEMATICS No. 365-198S75, DATE 05-15-74 for 1975 F-100 - 350. These can still be obtained from HELM, Inc. In Highland Park, MI. Well worth the money, IMHO.

First the FUEL SELECTOR SWITCH is a DPST (Double Pole-Single Throw) located inside the Heater/AC control faceplate. The UP position is labeled AUX and the DOWN position is labeled MAIN. Throwing the switch will select the appropriate tank's sending unit for the fuel gauge AND (beginning in 1975 MY) it will either ENGAGE or RELEASE the solenoid coil on the FUEL TANK selector valve, permitting fuel to flow from the chosen tank.

The way the electric FUEL TANK selector is plumbed and wired (and therefore operates) is as follows:

A) The AFT (behind the axle) tank flows when NO power is applied to the solenoid. This corresponds to the DOWN or "MAIN" position on the selector switch. This makes sense, in that the failsafe mode (as in a potential loss of power to the solenoid valve) results in the MAIN or AFT (behind the axle) being routed to the engine.

B) The AUX (midship - mounted on driver's side) tank flows when POWER is applied to the solenoid selector valve. This corresonds to the UP or AUX position of the selector switch.

C) Normally a DPST switch would have six (Count 'em -6) poles or wires. In this case, the FUEL SELECTOR SWITCH connector only has five (5) wires:

The SELECTOR SOLENOID VALVE (located just aft of the cab on the driver's side frame rail) only requires two terminals: RED-YELLOW-640 is key-switched B+ (12 V) power and BROWN-WHITE-674 is routed to the solenoid valve coil. The solenoid coil is grounded, completing the flow path. The second wire is not required because the valve DEFAULTS to the MAIN tank when there is NO POWER present.

The GAUGE side of the switch uses three terminals: ORANGE-286, GREEN-673, and GREEN-RED-675. ORANGE-286 runs from the switch to the Fuel Gauge, GREEN-673 runs to the AFT tank sending unit. GREEN-RED-675 runs to the MIDSHIP tank.

Note: the numbers (following the wire color) are Ford's circuit descriptor, as noted on the FACTORY Schematic.

It's easy to verify the operation of the solenoid selector valve. You can hear it engage and disengage with the operation of the selector switch (assuming the your engine is not running. (If you can't hear it -- have someone else operate the switch in the cab with the IGN KEY "ON"), while you listen under the vehicle. If BOTH the sending units are working properly (and the tanks each have different levels), the fuel gauge reading should also change when the selector switch is moved.

 

The back and forth on this topic was incredible. Thank you LeeSki for your detailed information!

 

Wow, I'm bleary eyed reading this thread. My stock, original 78 F150 Ranger Lariat has both working tanks since new. The "main" switch position allows fuel from, and reads level in forward or saddle tank. The "aux" = rear tank.

 

As it should. See excerpt from 78 owners manual below.

 

Thats what my manual says too. But everyone seems so confused.

 

I believe after reading through this that Ford must have changed their designations without thought to who it would confuzzle. It's likely that, at least in part, after there were no longer any in-cab tanks ('77-ish) that the forward-most tank, and also the larger of the two tanks, would become the MAIN tank.
At least it's larger by quite a bit on my '79. What about others? Were the big rear tanks ever available on standard trucks? Or only the Broncos and/or Camper Specials?
Were Camper Special trucks ever rear-tank only? Seems like they were, but I'm not sure. It's simple to name a tank when there is only one of course, but the location of that single tank might vary per model in that case too.

Does anyone here have a '78 or '79 standard or super-cab (non Camper Special and non cab/chassis) truck with only the single tank? I'm guessing most had duals, at least that I've seen, but certainly there were some with just a single. If so, then which one was it?
I think that would verify that there was a change in the nomenclature (if that's the proper terminology?) at that point.

In earlier years, when some models had only under-bed tanks, but others still kept the in-cab tanks, the in-cab would have remained the "main" tank presumably. But what about those early trucks with just one under-bed tank? Which one was it again? I think someone mentioned that.

But either way, I'm betting on Ford having changed the way they look at it. A simple and logical change in my mind. But that change has become a confusion point.
Is that out of line? Seems like the OE's and especially Ford didn't mind doing that kind of stuff. Just look at model year paint colors and names and codes and their inconsistencies!

Paul

 

I completely agree that ford changed their designations. The midship tank was an add-on in early models, and hence the "aux" tank. So there's confusion because the answer is "it depends......"

 

Well this thread certainly makes it all clear.

 

Hah! Yeah, ain't clarity a beautiful thing? But more importantly, ignorance is still bliss!

Paul

 

mine has Aux up main down.

 

After reading this thread, I'm with you.

 

Here's one for ya! My 76 Ranger Super Cab has a filler for an "in cab" tank that doesn't go anywhere (not connected inside the cab to anything) and the only usable tank (the ONLY tank) is between the rear frame rails (where the spare tire can usually be found) with two ungodly 90° bends that make fuelling at anything other than a trickle impossible and bad on the paint (in my case "petina"). So my query is this: WTF?!?!? I have personally put in 38 gallons ( was told that's what it held). It looks like an aftermarket tank, welded steel box with the filler between the frame and bed at another unholy angle. No selector switch on A/C panel. WHERE DID THEY MOUNT THE SPARE?!?! Any ideas anyone?