I have a '74 F-100 with the Main and Auxillary tank option but the main(rear-mounted one) does not work. The fuel gauge does not work at all and neither does the dash switch. I have no idea where to begin. It also does not help Mickey has gotten to this truck if you know what i mean, nothing seems to be in the right place. The fuel tank switch is located left of the steering wheel under the light switch, but when I move it to "Main tank" nothing happens, truck still runs from Auxillary tank. Help anyone?

 

first make sure you have 12 volts from switch to tank selector valve. The switch should send 12 v in one posititin and nothing in the other. If thats the case you likley have a bad selector valve. You can test it by taking the hoses off and blow into valve ( simulating gas flow) with switch in one position then filp switch and see if valve either opens or closes. If all that checks out you have a cloged fuel line or a bad pickup in the tank. AS for the sender take the wire off of the top of the sender and ground it to the frame. then with the key on see if needle on gauge pegs to the right , if so wiring is OK and problem is with sender...clear as mud??

 

On my truck I have the selector switch on the dash but there is also a valve behind the driver side seat. Not sure if that helps at all