1979 Fuel Tank Issue-Help
 

Ok, just to be clear, i replaced the solenoid switch on the frame rail as only the right tank was working before, but i replaced that months ago and things were working just fine. But long story short, once i replaced that the solenoid switch both tanks were switching back and further just fine, then recently this started, when running on left tank it decides it does want to run off of that tank.......Keep in mind i'll run on the left tank for weeks and all of a sudden it stops drawing fuel from that tank for some odd reason, just happens out of the blue...... it runs on the right side all the time just fine, but i want to fix the issue as i travel distances with the pickup from time to time.

Do i have a bad switch inside the cab?
Is the solenoid switch on the frame rail bad?
Could i have a bad ground some where?

Thanks for the help and feed back in advanced!

Doug

Re: 1979 Fuel Tank Issue-Help
 

You need to test it with a meter.
It could be the switch or valve or the wiring.

Power to the valve runs from the fuse panel to the switch and from there to the single terminal on the valve.

Before loading the parts cannon I'd check the connections for corrosion or loose terminals at the valve, switch, and fuse panel in that order.
I'd also make darn sure the valve is getting a good ground at the mounting bolts. If the frame is crusty it might not be making good contact. Set your digital volt meter for DC Volts in the 20V range.
Test the voltage directly on the battery posts then move the ground to the engine and the frame to give yourself a real world look at the battery cable condition. If the engine or frame show more than a .3VDC difference from direct to the battery you probably need to clean up your cables or replace them but that's up to you.
Climb under and clip the positive meter lead to the Starter BAT stud and probe the metal body of the valve for voltage using the negative meter probe. Assuming the battery cables are in good shape it should read darn close to full battery voltage... or at least the reading you got between the battery positive and the frame... within .2 to .3 VDC. If it's more than .3vdc lower clean up around the mounting bolts and add star washers next to the frame and the valve when you re-install the bolts.

The switch is fairly easy to test.
Switch the ignition on.
Ground the meter Ground probe.
Test the Red wire at the switch for volts. It should be close to battery voltage.
Flip the switch to the AUX position and check voltage at the Green wire. Lower voltage or no voltage means the switch is not in good shape.

You also should check the molded connector at the valve for the teltale green puss from corrosion. If the stud on the valve is a #10 machine screw you can clean the molded connector out with a .17 calibre bronze bore brush. If it's a #8 machine screw you'll need to find other means of clearing the corrosion. Crunching a bore brush down slightly by forcing it through a #8 nut on a drill would probably do it. Clean the connector by hand... DO NOT clean the connector with the brush in a drill.

Re: 1979 Fuel Tank Issue-Help
 

wow thank you for all the details. Wiring and i have a history together, but you spelled this out perfectly. Thank you, thank you very much!

Re: 1979 Fuel Tank Issue-Help
 

Sounds more like a blockage or restriction in the tank.
Sure there's not something floating around in the tank???
If its to big to be pulled into the pickup it will stick to the opening until you switch tanks to give it time to move away from pickup.

Re: 1979 Fuel Tank Issue-Help
 

If you install the pickup sock this will never happen.
If the sock is missing or deteriorated it's possible.