How do you change a heater core in a 1976 F250 Ford pickup?

To change the heater core in a 1976 Ford F250 pickup, first disconnect the battery and drain the coolant from the radiator. Remove the dashboard and any components obstructing access to the heater box, which is typically located on the passenger side. Unbolt the heater core from the heater box, replace it with the new core, and reassemble everything in reverse order. Finally, refill the coolant and check for leaks before reconnecting the battery.