The GMC K3500 brake light utilizes 1157, 2057, and 3057 bulb sizes depending on the specific production period for the heavy duty truck. Available technical data covers the historical span 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 K3500 brake light specifications cover three bulb types across the main brake light position: the 3057, 1157, and 2057. All three conform to ANSI standards applicable in both the United States and Canada.
The 3057 is a dual-filament wedge bulb in a T25 form factor, rated at 12V with a high filament draw of 27W and a low filament draw of 7W. It is the most frequently specified brake bulb for the GMC K3500, appearing across the 1990-1992 and 1996, 1998-2000 model years.
The 1157 uses a BAY15d bayonet base rather than a wedge mount, which makes it physically incompatible with sockets designed for the 3057. It operates at 12V with filament ratings of 21W and 5W, and it fits the K3500 for the 1979-1982, 1993-1995, and 1997 model years.
The 2057 also uses a BAY15d bayonet base and is described as a brighter variant of the 1157, with filament ratings of 26.9W and 8W at 12V. It is specified for the K3500 across the 1983-1986 and 1988-1989 model years.
Because the 1157 and 2057 share the BAY15d bayonet base, they are physically interchangeable at the socket level, though their wattage outputs differ. The 3057, as a wedge-base bulb, is not socket-compatible with either the 1157 or 2057.
The 1997 GMC K3500 is a notable fitment case: the main brake light position calls for the 1157, while surrounding model years (1996 and 1998) specify the 3057. These two bulb types use different base designs and are not interchangeable.
The Center High Mount Stop Light (CHMSL) on the GMC K3500 uses either the 921 or the 912, both of which are T15 wedge bulbs rated at 12V. The 921 is rated at 16W, while the 912 is a lower-wattage variant at 12W.
The 912 appears in the CHMSL position only for the 1998 K3500, while the 921 is specified for the 1993-1997 and 1999-2000 model years. Although both share the T15 wedge form factor, their wattage difference means they are not identical replacements.
All bulb types listed across both the main brake light and CHMSL positions are dual-filament or single-filament ANSI-standard bulbs, a classification that reflects standardized electrical and physical specifications shared across North American automotive applications.
The main brake light socket type changed at least three times across the K3500's production span, moving between the BAY15d bayonet base and the T25 wedge base at various model year intervals, which makes year-specific verification necessary before replacement.