GMC Sierra Turn Signal Bulb Size

Additional Notes

• The T25 wedge format is the most frequently specified bulb body type across the GMC Sierra's turn signal positions, appearing in multiple variants including the 3157, 3157NA, 4157NA, 5702AK, 3047, and 3157 across front and rear positions from 1999 through the mid-2010s.
• The 7444NA is a natural amber T20 dual-filament wedge bulb rated at 12V and 21W/5W. It serves as the front turn signal bulb for the GMC Sierra 1500 from 2019-2022, and also covers both the 2021 rear turn signal and the 2023-2024 rear turn signal positions.
• The "NA" suffix across multiple bulb designations, such as 3157NA, 4157NA, and 7443NA, indicates natural amber glass rather than a clear envelope with a separate amber lens. This distinction affects whether the amber color is produced by the bulb itself or by the vehicle's housing.
• The 5702AK is a Sylvania-specific part number for an amber-coated variant of the ANSI 3157 bulb. It shares the T25 dual-filament format and 12V/27W/7W rating with the 3157 family but achieves its amber color through a coating rather than natural glass or a housing lens.
• The 3047 is a single-filament T25 wedge bulb rated at 12V and 27W, distinguishing it from the dual-filament 3157 it replaced in the Sierra's rear turn signal position starting in 2007. A single-filament bulb serves only one lighting function, whereas dual-filament bulbs serve two, such as turn and running light combined.
• The GMC Sierra 1500 and 3500 HD trims frequently require different front turn signal bulbs within the same model year. In 2019-2020, the 1500 uses the 7444NA while the 3500 HD uses the 7443, and in 2014 the 1500 uses the 7443 while the 3500 HD uses the 4157NA.
• In 2016-2018, the Sierra 1500 front turn signal fitment is conditional on headlamp type, with the 7443NA specified for 2016 and 2018 and the 7444NA for 2017, all restricted to configurations with HID headlamps. The 3500 HD in those same years uses the 7443 regardless of headlamp type.
• The 7443 and 7444NA share the same T20 wedge format and 12V/21W/5W electrical rating, but the 7444NA incorporates natural amber glass. These two bulbs are not interchangeable in applications where the housing relies on the bulb itself to produce the amber color required for turn signal compliance.
• The 12961 is a Philips-designated T10 miniature wedge bulb with a W2.1x9.5d base, rated at 12V and 5W. It is specified exclusively for the Front Outer Turn Signal position on the GMC Sierra in 2000-2002, and its "Side, Export" notation indicates it applies to a side-mounted position intended for markets outside North America.
• The front turn signal position on the GMC Sierra transitioned from the T25-based 3157NA (1999-2006) to the T25-based 4157NA (2007-2013 in most configurations) and then to the T20-based 7443 or 7444NA family from 2014 onward, reflecting a shift to a physically smaller bulb format in later model years.