GMC K2500 Headlight Bulb Size

Additional Notes

• The H6054 is the most consistently specified bulb across the GMC K2500 headlight data, appearing in both high beam and low beam positions from 1979 through 2000. It is a 5x7-inch rectangular sealed beam unit operating at 12V, conforming to ANSI standards for the US and Canada. As a sealed beam design, the entire unit is replaced rather than an internal bulb.
• For model years 1992-2000, the GMC K2500 with halogen capsule headlamps uses the 9005 for high beam and the 9006 for low beam. These are separate single-filament halogen bulbs and are not interchangeable with each other. The 9005 carries a P20d base at 65W, while the 9006 uses a P22d base at 55W, meaning the base fittings are physically distinct.
• The H6054 sealed beam unit serves dual duty across both high beam and low beam positions on two-headlamp configurations throughout the full model range. This is a characteristic of sealed beam systems, where a single unit contains the reflector, lens, and filament as one assembly.
• On 1988-1991 four-rectangular-headlamp configurations, the high beam position uses the H4701 and the low beam uses the H4703. Both are 7-inch round sealed beam units operating at 12V, but they are distinct part numbers assigned to separate beam functions and are not listed as interchangeable.
• For 1982-1986 four-headlamp configurations, the low beam position is covered by either the H4656 or H4652 depending on the year, while the high beam uses the H4651. All three are 4x6-inch rectangular sealed beam units at 12V. The H4652 is noted as a variant of the H4651, and the H4656 is a separate 4x6-inch unit, so substitution across these part numbers is not supported by the specifications.
• The 1979-1980 GMC K2500 with two round headlamps uses the H6024, a 7-inch round sealed beam unit at 12V, for both high and low beam positions. This contrasts with the rectangular H6054 used on two-rectangular-headlamp configurations of the same years, making headlamp housing shape a determining factor in the correct sealed beam selection.
• Halogen capsule headlamp configurations, which use the 9005 and 9006 bulbs, are listed alongside sealed beam options from 1988 through 2000, indicating that the K2500 was offered with more than one headlamp system type during that period. The sealed beam and halogen capsule systems require entirely different replacement parts and are not compatible with one another.
• All bulb types listed across the K2500 specifications conform to ANSI standards applicable in the US and Canada, and all operate at 12V. The sealed beam units, including the H6054, H4701, H4703, H4651, H4652, H4656, and H6024, do not have replaceable internal bulbs, distinguishing them fundamentally from the 9005 and 9006 halogen capsule bulbs, which are serviceable as individual components.