When I switch from main tank to aux. tank in my 78 F150, the gauge goes to empty and the truck sputters and dies. It has a full tank of gas in it. It appears to be more than just a valve/solenoid problem as the gauge goes to zero. I doubt that the tank has dirt or junk in it, otherwise it would read full and not get any fuel. Can some one help me? Also where is the valve to switch tanks, as the switch on the dash next to the heater is an electrical switch and not the valve

 

I'm not familiar with the electric solenoid operated valves, but if your tank is full and the truck dies when you switch to this tank then its either the valve is not actually getting switched all the way or the line is in fact clogged. Try tracing the fuel line back from the front of the vehicle. You should find the switch that way. I would remove the line going to the auxilliary tank and blow some air back into the tank. If there is blockage it should clear it at least temporarily. If no blockage then suspect the valve is faulty. You may also need to verify the electric connections are all doing their job too. I hope this helps some at least.

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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Another thing to check is that your fuel line is not cracked/rotted. I had that problem with my 72, with age simply getting the better of the fuel line. It wouldn't hurt to check the condition of your lines while checking the valves and lines for blockage.

 

I would bet that you have a wire pulled loose at your switch or the solenoid it self, since your gauge is reading empty also. you may also have a bad fuel pickup in the tank, I believe that the pickup and sending unit are one piece on those.
hope this helps. let us know what you find.

 

The valve is mounted just forward of the aux tank on the frame cross-member.