How do you change a heater core in a 1988 Isuzu pick up?

To change the heater core in a 1988 Isuzu pickup, start by disconnecting the negative battery cable and draining the coolant from the radiator. Remove the dashboard or any components obstructing access to the heater core, typically located in the firewall. Disconnect the heater hoses from the core, unbolt it from its housing, and replace it with the new unit. Finally, reassemble everything, refill the coolant, and check for leaks.