1979 Fuel Tank Issue-Help

[ddc456]

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