1969 F100 AUX tank question

[Gaslight]

On my truck the AUX tank switch in the floor just says "AUX" or "Off". Is "Off" position pulling from the main tank in the cab?

Jake

[basketcase0302]

I'm amazed it only has those two selections Jake.
The one on my 71' F-350 DRW with dual tanks had a Ft / OFF / RR for selections and I thought it was OEM.
Maybe someone else can chime in here soon.
The drawing shows the valve but of course not the selection(s):

[390FE1972]

My selector switch has off, main, and aux. You might want to look at the plate near the two bolts to see if it is hidden under the carpet in your picture.

Regards

[Gaslight]

I've cleaned the plate up while cleaning the truck further. Its just those two selections. Right now I am driving it in the "off" position. As soon as I notice the gauge drop I can verify that it is on the main. I seem to be able to pull from the "aux" tank fine. But the gauge does not seem to be reading. So it will have to come down at some point.

Jake

[zgerbic]

I would think it should not be too hard to figure this all out. In general the valve should have two inputs, aux and main, and one outlet to the fuel pump. should be able to see from the bottom of the truck. It is possible it is an aftermarket valve and off is really main, and there is no actual off position. The valve would need to have a rotary switch on it in order to change which gas sender is attached to the gas gauge. I suspect there is no switch or it is not connected to switch between senders. Again there should be wiring at the valve itself to make this change.

[basketcase0302]

=zgerbic
I would think it should not be too hard to figure this all out. In general the valve should have two inputs, aux and main, and one outlet to the fuel pump. should be able to see from the bottom of the truck. It is possible it is an aftermarket valve and off is really main, and there is no actual off position. The valve would need to have a rotary switch on it in order to change which gas sender is attached to the gas gauge. I suspect there is no switch or it is not connected to switch between senders. Again there should be wiring at the valve itself to make this change.

Pretty sure you nailed it with being aftermarket as every single dual tank setup I've seen on our bumps had the tank sending unit selector switch mounted on the dash below the instrument cluster.



And every factory switch I'd ever seen was mounted in this exact location.

[Gaslight]

I have the dash switch as well. For the gauge to read from the correct tank. If it is an aftermarket setup they really went all the way. All the AUX tank stuff that should be there is.

Jake

=zgerbic
I would think it should not be too hard to figure this all out. In general the valve should have two inputs, aux and main, and one outlet to the fuel pump. should be able to see from the bottom of the truck. It is possible it is an aftermarket valve and off is really main, and there is no actual off position. The valve would need to have a rotary switch on it in order to change which gas sender is attached to the gas gauge. I suspect there is no switch or it is not connected to switch between senders. Again there should be wiring at the valve itself to make this change.

Pretty sure you nailed it with being aftermarket as every single dual tank setup I've seen on our bumps had the tank sending unit selector switch mounted on the dash below the instrument cluster.



And every factory switch I'd ever seen was mounted in this exact location.

[basketcase0302]

Memory fresher after coffee this AM LOL..
I owned a 1971 Winnebago that was built on a P-350 Ford chassis, (6 cylinder 300 engine / C-6 transmission / D-70 rear axle).
It had dual tanks that had a different tank selector that looked just like the one you've pictured only having the two different positions.
But like 390 or zgerbic posted above you might have to unhook the fuel lines underneath to trace the flow for each position.
Seems like mine was "opposite" if memory serves me right, (arrow pointing one way-meant the flow was through the opposite port under the truck cab)?

[Gaslight]

Yeah I will either work it out by driving it or dropping the AUX tank which it looks like I am going to have to do at some point. I just blew a passenger rear wheel cylinder. So now its all new brakes on the rear! But given what I saw when I pulled the drums I am thinking "thank god that cylinder blew!"

Jake

[Fraser]

The 3 position valve seems odd to me, why even have an off? But that is what mine has as well. My thought is that someone has replaced the valve at some point. and just put a 2 position one in.
Maybe the middle is for theft prevention, When I worked at a Ford dealership, in 1977, they still had one new Bronco, it ran out of gas, and no one could figure out why it wouldn't switch over! After a couple of hours, an older salesman pointed out the valve on the floor, and they all had a good laugh. Anyway, I think that Bronco was only 2 position, so maybe that's the valve you have. The doc. library may have a picture of what was original, in a sales brochure.

[Mach428]

The electric selector switch is factory and for the gauge itself; nothing to do with the actual fuel routing. The selector valve has THREE positions as mentioned. You can look under your truck and see there are fuel lines that run to each tank and forward to the fuel pump. You should be able to move the valve to three different positions. There’s nothing “after market” about this set up.