How do you replace the headlight bulb located on a 1999 Ford Expedition?

Push headlight retaining housing retaining clips (rectangular metal tabs located above radiator wall and to outside and rear or headlight)rearward, then upward to release headlight assembly. Pull headight assembly forward from body. Unscrew bulb retaining ring. Remove bulb from headlight housing. Remove bulb from socket wiring by pulling straight out. Insert new bulb into socket wiring (use paper towel to avoid touching bulb). Reinstall by reversing removal instructions.

you also may have to loosen the air filter assembly and remove the air intake flange (rubber part) to gain full access to the screw holding the coolant tank.