The GMC K2500 brake light utilizes 1157, 2057, and 3057 bulb sizes for various lighting applications across the different production versions of the vehicle. Available technical data covers the specific time range from 1979 through 2000 for the components listed in the provided specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The GMC K2500 brake light circuit relies on three bulb types across its model history: the 3057, 1157, and 2057. All three are dual-filament bulbs rated at 12 volts, designed to serve both the brake (high-intensity) and tail (low-intensity) functions from a single housing.
The 3057 is the most frequently specified brake bulb for the GMC K2500, covering the 1990-2000 model years with the exception of 1992-1996. It uses a T25 wedge base and operates at 27W on the brake filament and 7W on the tail filament.
The 1157 uses a BAY15d bayonet base and is rated at 21W/5W. It is specified for the K2500 in 1979-1982, 1993-1994, and 1996, making it incompatible as a direct substitute for the wedge-base 3057 despite serving the same electrical function.
The 2057 also uses a BAY15d bayonet base and shares its physical form with the 1157, but operates at a higher output of 26.9W on the brake filament and 8W on the tail filament. It is specified for the K2500 from 1983-1989.
Although the 2057 and 1157 share the same BAY15d bayonet base, they are not identical in wattage output. Substituting one for the other may affect brightness levels, and compatibility with the original socket should be confirmed before replacement.
The 3057 wedge base and the BAY15d bayonet base used by the 1157 and 2057 are physically incompatible. A socket designed for one base type will not accept the other, making cross-substitution between these groups impossible without a socket adapter.
The Center High Mount Stop Light (CHMSL) on the GMC K2500 uses single-filament wedge bulbs rather than the dual-filament types found in the main brake lights. This reflects the CHMSL's dedicated stop-light-only function, which requires no tail-light filament.
The 921 is specified for the K2500 CHMSL across 1993-2000, with the sole exception of 1998. It is a T15 wedge bulb rated at 12V and 16W.
The 912 is specified exclusively for the 1998 K2500 CHMSL. It is also a T15 wedge bulb but is rated at 12W, making it a lower-wattage variant of the 921. Both share the same wedge base form factor.
Because the 912 and 921 share the T15 wedge base, they are physically interchangeable in the socket, but their wattage ratings differ. Installing a 921 in place of a 912, or vice versa, may not conform to the original factory specification for that model year.