The Ford Bronco II used two distinct headlight types across its production run: the H6054 sealed beam unit from 1984-1988 and the 9004 halogen bulb from 1989-1990.
The H6054 is a 5x7-inch rectangular sealed beam unit, meaning the lens, reflector, and filament are fused into a single glass assembly. When the filament fails, the entire unit requires replacement rather than just an internal bulb.
The 9004 is a dual-filament halogen bulb with a P29t base, operating at 12V with a 65W rating for high beam and 45W for low beam. A single bulb serves both functions through its two filaments.
Both the H6054 and 9004 are ANSI-standardized types recognized in the United States and Canada, meaning fitment follows a defined specification rather than a proprietary design.
On the Ford Bronco II, the same bulb size applies to both the high beam and low beam positions for any given model year, as the 9004's dual-filament design handles both functions within one unit, and the H6054 sealed beam operates the same way.
The transition from H6054 to 9004 between the 1988 and 1989 model years represents a change in headlight technology, from a sealed beam assembly to a replaceable halogen capsule housed within a separate reflector and lens.
The H6054 and 9004 are not interchangeable. The sealed beam format of the H6054 and the socket-mounted capsule format of the 9004 require different headlight housings entirely.