The GMC R2500 front turn signal requires a 2357NA or 2057NA bulb size, while the rear turn signal uses a 2057 bulb size. The replacement chart covers 1987 to 1989 model years with corresponding bulb specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The GMC R2500 front turn signal uses the 2357NA for 1988-1989 and the 2057NA for 1987.
The rear turn signal across all three model years, 1987-1989, uses the 2057 bulb.
All three bulb types found in these specifications, the 2357NA, 2057NA, and 2057, share the BAY15d bayonet base, meaning the physical mounting interface is identical across all positions and years.
The BAY15d base is a double-contact bayonet fitting, which supports dual-filament operation by carrying separate circuits for the high-wattage and low-wattage filaments within a single bulb.
Each bulb in these specifications operates at 12 volts with a dual-filament wattage rating of 26.9W for the high-intensity filament and 8W for the low-intensity filament.
The 2057NA and 2057 are described as brighter variants of the 1157, indicating higher output from the primary filament despite sharing the same wattage rating and base type as the 1157.
The "NA" suffix on the 2357NA and 2057NA denotes natural amber glass, meaning the amber color is produced by the glass coating rather than by an external amber lens.
The 2057 used in the rear turn signal position carries no amber glass coating, making it a clear-glass bulb that relies on the vehicle's lens for color output.
All bulbs listed conform to ANSI standards recognized in both the United States and Canada, indicating standardized electrical and photometric performance requirements.
Although the 2357NA and 2057NA share the same base, wattage, and voltage ratings, they are specified for different model years in the front turn signal position and are not listed as interchangeable within these specifications.