Hello,
My 1994 7.5 liter F-350 4x4 rear fuel tank stopped working. Plus, front fuel tank pumps gas into the rear tank in tell it overflows.
Dash switch seems OK.
Next I'm going to drop rear tank and replace fuel pump???...

A few things here, there is apparently an issue (as usual) with the check valve allowing fuel to pass into the wrong tank. It also would seem the rear pump is not turning on.

Now, as to the switch, what makes you say it is actually working? Not saying it isn't, just wanting to see what you have done to validate it is functioning.Have you done actual testing, or guessing due to the gauge changing? They are separate circuits... The switch does need ot be validated for function, as it is the main mechanism to direct power to the fuel pumps. You can also check for power to the rear pump to be certain it is getting power. I would recommend such before going through the work of getting to the pump. It isn't uncommon for the pump to go out, but neither is it uncommon for there to be issues with the switch.