There's also usually an isolator (looks like a Ford starter solenoid) that separates the house and chassis circuitry on these Fords, typically on the fender or firewall, and an associated Momentary On Push button in the cab somewhere, that normally keeps the house and chassis electrical system separate, but ties them together when the button is pushed. These can fail or have corroded contacts, that can inhibit charging the house battery. Measure the voltages on that solenoid when plugged into shore or generator power as well.
