The GMC K1500 brake light utilizes unique bulb sizes 3157, 3057, 1157, and 2057 depending on the specific version of the vehicle. Available data covers the range from 1979 through 1999 for the components listed.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The GMC K1500 brake light specifications cover two distinct sub-parts: the standard brake light and the Center High Mount Stop Light (CHMSL), each drawing from a separate set of bulb types across their respective model years.
The 3057 is the most frequently specified brake bulb across the K1500 lineup, appearing in nine model years spanning 1990-1996 and 1998. It is a dual-filament wedge bulb in the T25 form factor, rated at 12V with a 27W bright filament and a 7W dim filament, and meets ANSI standards for the US and Canada.
The 3157 and 3057 share identical voltage and wattage ratings (12V, 27W/7W) and both use the T25 wedge form factor under ANSI standards. Despite these similarities, they are distinct part numbers and are not confirmed as interchangeable within these specifications.
The 1157 uses a BAY15d bayonet base rather than a wedge base, which makes it physically incompatible with sockets designed for T25 wedge bulbs such as the 3057 or 3157. It is rated at 12V, 21W/5W, and appears in the K1500 brake light position for 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 12V, 26.9W/8W versus the 1157's 21W/5W. It is specified for the GMC K1500 brake light position across 1983-1986 and 1988-1989.
Because the 1157 and 2057 share the BAY15d bayonet base, they occupy the same socket type, though their differing wattage ratings distinguish them as separate specifications within the K1500's history.
The CHMSL on the K1500 uses single-filament wedge bulbs in the T15 form factor, a physically smaller category than the T25 bulbs used in the standard brake light position.
The 921 is the predominant CHMSL bulb, specified for 1993-1997 and 1999. It is rated at 12V and 16W under ANSI standards.
The 912 appears solely in the 1998 K1500 CHMSL position. It is a T15 wedge bulb rated at 12V and 12W, making it a lower-wattage variant compared to the 921's 16W rating, despite sharing the same base type.
The wattage difference between the 912 (12W) and the 921 (16W) indicates they are not direct substitutes, as output levels differ even though both are T15 wedge bulbs meeting the same ANSI standard.