The GMC C3500HD brake light requires bulb sizes 3057 and 1157 for proper illumination of the rear lighting system. Data for the specified vehicle covers the range from 1991 through 2002.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The GMC C3500HD uses the 3057 bulb as its brake light across the widest span of model years in these specifications, covering 1991-1992 (Medium Duty trim) and 1994-2002.
The 3057 is a dual-filament T25 wedge bulb rated at 12V with a 27W high filament and a 7W low filament, conforming to ANSI standards for the US and Canada.
The dual-filament design of the 3057 allows it to serve both a brighter stop function and a dimmer running light function within a single bulb housing.
The 1993 GMC C3500HD brake light specification calls for the 1157 bulb rather than the 3057 used in surrounding model years, making it a distinct fitment for that year.
The 1157 uses a BAY15d bayonet base, which is physically incompatible with the wedge socket required by the 3057, meaning the two bulbs are not interchangeable despite both being dual-filament 12V types.
The 1157 is rated at 21W/5W, giving it a lower wattage output on both filaments compared to the 3057's 27W/7W rating.
The 1991-1992 brake light entries carry a Medium Duty designation, indicating the 3057 fitment applies specifically to that trim classification for those years.
The center high mount stop light on the GMC C3500HD uses the 921 bulb across all listed years, spanning 1993-2002.
The 921 is a single-filament T15 wedge bulb rated at 12V and 16W, conforming to ANSI standards for the US and Canada.
Because the 921 is a single-filament bulb, it functions solely as a stop light rather than serving a combined stop and running light role.