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I'll try to explain best I can, 67 F250 fuel gauge doesn't work either tank, the switch & plug which connect to it have 6 wires & terminals, I have continuity between top center terminal & top right terminal on switch when switched to left tank side, top right terminal is lead from in cab tank, switch to right tank I have continuity between top center terminal & top left terminal , top left terminal is lead to fuel gauge, when I jump left & right upper terminal fuel gauge reads full, I just filled both tanks, try jumping all other wires from plug I get no other readings ,seems to me the center terminal should be the one to the gauge since it is the common denominator but far as I can tell there hasn't been any cutting and splicing except by me when I installed a Autometer Phantom gauge, The stock fuel gauge has never worked since I owned the truck , the diagram from the fordification site isn't overly clear.I disassembled switch & cleaned the terminals & didn't see anything amiss inside.
I found a better diagram & I am correct that the upper center terminal is supposed to go to the gauge, the bottom 3 terminals are for a electric pump which I don't have , Now I just have to find where someone crossed the wires
I'll try to explain best I can, 67 F250 fuel gauge doesn't work either tank, the switch & plug which connect to it have 6 wires & terminals.
I have continuity between top center terminal & top right terminal on switch when switched to left tank side, top right terminal is lead from in cab tank, switch to right tank.
The diagram from the fordification site isn't overly clear.
The diagram on Fordification (it's from the 1964/72 Ford Truck Parts Catalog) does not relate to your truck, because the right and left saddle tanks you have are not genuine Ford.
Ford never offered saddle tanks for any truck. The only optional auxillary tank offered for 1967/72's was the 25 gallon tank that fits inside the left frame rail.
Stylesides: The exposed fuel cap pokes thru the bed side in front of the left rear wheel above the scallop line on 1967/69's, in front of the rear wheel below the scallop line on 1970/72's.
You may have the fuel caps behind aluminum doors that rivet to the bedsides, as that was the usual procedure with aftermarket fuel tanks.
Here in SoCal, the Fey Bumper Co. installed saddle tanks on trucks of this vintage for dealers/owners.
When I first got my 69 F250, the gauge wouldn't work for either tank but all wiring seemed to test OK. On a hunch, I rapidly worked the switch back and forth 20-30 times and the gauge started working. Dirty/corroded contacts in the switch. It's been fine ever since.
My $.02,
Gene
I wrang out the wires & found where someone { NOT ME REALLY} crossed them up, also discovered sending unit on frame tank is inop luckily I have a spare that I hooked up & gage works so in cab tank works great after I run the frame tank empty will swap out units & should be ok