GMC B6000 Headlight Bulb Size

Additional Notes

• The GMC B6000 headlight specifications across the 1980-1991 model years reference three sealed beam form factors: the 5x7-inch rectangular H6054, the 7-inch round H6024, and the 4x6-inch rectangular units H4651 and H4656. All four types conform to ANSI standards recognized in the United States and Canada and operate on 12V electrical systems.
• All bulb types listed for the GMC B6000 are sealed beam units, meaning the lens, reflector, and filament are fused into a single assembly. When a filament fails, the entire unit requires replacement rather than an internal bulb swap.
• The H4651 and H4656 share the same 4x6-inch rectangular sealed beam form factor but serve different functions. The H4651 is designated for the high beam position, while the H4656 is designated for the low beam position in four-lamp rectangular headlamp configurations. The two types are not interchangeable despite their physical similarity.
• In four-lamp rectangular headlamp configurations, the B6000 uses H4651 units for high beam and H4656 units for low beam across model years 1980-1988, with each position requiring its specific sealed beam type.
• The H6054 5x7-inch rectangular sealed beam functions as a dual-purpose unit, serving both high beam and low beam positions in two-lamp rectangular headlamp configurations. This contrasts with the four-lamp setup, where dedicated high and low beam units are used separately.
• Similarly, the H6024 7-inch round sealed beam handles both high and low beam functions within two-lamp round headlamp configurations, appearing in both sub-parts of the specifications for the same model years.
• For model years 1989-1991, the specifications list only the H6054 for both high and low beam positions, indicating those years of the B6000 used exclusively the two-lamp rectangular headlamp configuration without alternative lamp arrangements.
• The 1988 model year is the only year in the specifications where all three headlamp configurations, two-lamp round, two-lamp rectangular, and four-lamp rectangular, are listed simultaneously, reflecting that multiple headlamp arrangements were available on the B6000 in that year.