How do I replace a 1989 ford econoline heater core?

To replace the heater core in a 1989 Ford Econoline, start by disconnecting the battery and draining the coolant from the radiator. Next, remove the dashboard and the heater box to access the heater core, which is typically located behind the dashboard. Disconnect the hoses attached to the heater core, remove the old core, and install the new one in reverse order. Finally, reassemble the dashboard, refill the coolant, and check for leaks.