The GMC R2500 Suburban front turn signal requires a 3057NA or 2057NA bulb size, while the rear turn signal uses a 2057 bulb size. The replacement chart covers 1987 through 1991 production 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 Suburban front turn signal uses the 3057NA bulb for the 1989-1991 model years and the 2057NA for the 1987-1988 model years, indicating a change in front turn signal bulb specification at the 1989 model year.
The 3057NA is a dual-filament wedge bulb in the T25 form factor, rated at 12V with a 27W high filament and 7W low filament, and features natural amber glass that produces a colored output without the need for an amber lens.
The 2057NA shares the same 12V, 26.9W/8W dual-filament configuration and natural amber glass as the 3057NA but uses a BAY15d bayonet base rather than a wedge base, making the two bulbs physically incompatible despite their similar electrical ratings.
Because the 3057NA uses a wedge base and the 2057NA uses a BAY15d bayonet base, these two front turn signal bulbs are not interchangeable across the 1988 and 1989 model year boundary, even though their wattage ratings are close.
The rear turn signal on the GMC R2500 Suburban uses the 2057 bulb across all listed model years, 1987-1991, without any change in specification.
The 2057 and 2057NA share identical electrical ratings of 12V, 26.9W/8W and the same BAY15d bayonet base, with the sole distinction being that the 2057NA incorporates natural amber glass while the 2057 does not.
Both the 2057 and 2057NA are described as brighter variants of the 1157 bulb, meaning sockets designed for the 1157 are generally compatible, though output levels will differ.
The dual-filament design present in all three bulb types, 3057NA, 2057NA, and 2057, allows a single bulb to serve both a lower-intensity running or parking function and a higher-intensity signaling function within the same housing.
All three bulb types listed in these specifications conform to ANSI standards applicable in both the United States and Canada.
The rear turn signal specification remains the non-amber 2057 for all five listed model years, while the front positions use amber-glass variants, reflecting a design approach where amber coloring is handled at the bulb level in the front and presumably at the lens level in the rear.