can faulty fuel pump relay switch prevent back fuel tank from supplying gas on 1995 ford f150

Could be a faulty Fuel Relay Switch. If you replace, it be sure to thoroughly clean all contacts when assembling and spray with electrical contact spray. If that does not work, then you might drain and drop the tank that fuel is not pumping from and replace the In- Tank fuel pump. I have two of these classics (1987 & 1994)and the only problems I've ever had with them are along the same line as your issues. Once I was unable to sort things out on my 1987 and had to resort to taking it to my trusted Ford dealer to fix.