The GMC C2500 brake light utilizes 1157, 2057, and 3057 bulb sizes depending on the specific production requirements for the vehicle lighting system. Data for the lighting components spans the period from 1979 through 2000.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The GMC C2500 brake light circuit relies on three bulb types across its model years: the 3057, 1157, and 2057. All three are ANSI-standard 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 C2500, covering model years 1990-1996, 1998-2000, with the exception of 1997. It is a dual-filament wedge bulb in a T25 form factor, rated at 27W on the brake filament and 7W on the tail filament.
The 1157 uses a BAY15d bayonet base rather than a wedge mount, which makes it physically incompatible with sockets designed for the 3057. It is rated at 21W/5W and appears in the C2500 for model years 1979-1982, 1993, and 1997.
The 2057 also uses a BAY15d bayonet base and is described as a brighter variant of the 1157, rated at 26.9W/8W. It is specified for the C2500 for model years 1983-1986 and 1988-1989. Despite sharing the same base type as the 1157, the two bulbs differ in wattage output.
The socket base type is a critical fitment factor for the C2500. The 3057 wedge base and the BAY15d bayonet base of the 1157 and 2057 are not interchangeable, meaning a socket built for one base type will not accept a bulb of the other.
Model years 1993 and 1997 each use the 1157 while the surrounding years use the 3057. Because the 1157 and 3057 have different base types, substituting one for the other in those years is not a direct swap.
For the Center High Mount Stop Light (CHMSL), the GMC C2500 is specified across model years 1993-2000. This circuit uses single-filament wedge bulbs in the T15 form factor, distinct from the dual-filament bulbs used in the main brake lights.
The 921 is the predominant CHMSL bulb, rated at 16W, and is specified for model years 1993-1997 and 1999-2000. The 912 is specified solely for 1998 and is a lower-wattage variant of the 921, rated at 12W. Both share the T15 wedge form factor.
Although the 912 and 921 share the same T15 wedge base and are physically similar, their wattage ratings differ. The 912 produces less light output than the 921, which is a relevant distinction for a safety-critical lamp such as the CHMSL.
The brake light and CHMSL circuits on the C2500 use entirely separate bulb families. The main brake lights use dual-filament bulbs (3057, 1157, or 2057), while the CHMSL uses single-filament T15 wedge bulbs (921 or 912). The two groups are not interchangeable with one another.