GMC C2500 Headlight Bulb Size

Additional Notes

• The H6054 is the most widely used bulb type across the GMC C2500 headlight specifications, 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, and the entire unit is replaced rather than an internal bulb.
• From 1992 through 2000, the GMC C2500 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, as the 9005 uses a P20d base at 65W while the 9006 uses a P22d base at 55W.
• The 4-rectangular-lamp configuration on 1988-1991 models uses the H4701 for high beam and the H4703 for low beam. Both are 7-inch round sealed beam units, though they serve distinct beam functions and are not interchangeable between positions.
• The 4-headlamp configuration on 1982-1986 models uses 4x6-inch rectangular sealed beam units for the low beam position, with H4656 specified for 1982-1983 and 1986, and H4652 specified for 1984-1985. The H4652 is a variant of the H4651 and all are non-replaceable sealed units.
• The 1979-1980 models with 2 round headlamps use the H6024, a 7-inch round sealed beam unit at 12V. This type is distinct from the H4701 and H4703 round units used in later 4-lamp configurations, and the three are not listed as interchangeable.
• All sealed beam types listed across the GMC C2500 specifications conform to ANSI standards applicable in both the US and Canada, meaning the physical and electrical specifications are standardized rather than proprietary to the vehicle.
• The 1991 model year represents a transitional point in the specifications, where three distinct headlamp system types are listed simultaneously: a 2-rectangular-lamp sealed beam setup, a 4-rectangular-lamp sealed beam setup, and a halogen capsule system, each requiring different bulb sizes for both high and low beam positions.
• Because sealed beam units integrate the lens, reflector, and filament into a single assembly, the H6054, H4701, H4703, H4651, H4652, H4656, and H6024 types listed in these specifications are all full-unit replacements rather than individual bulbs that can be removed from a housing.