GMC Sierra Tail Light Bulb Size

Additional Notes

• The GMC Sierra outer tail light draws from four distinct bulb types across its model history: the 1156, 7443, 7444, 3047, and 3157, each representing a different combination of filament count, base design, and wattage.
• The 3157 is a dual-filament T25 wedge bulb rated at 12V with a 27W high filament and 7W low filament. It was the outer tail light bulb for the GMC Sierra from 1999-2006.
• The 3047 is a single-filament T25 wedge bulb rated at 12V and 27W. It shares the same T25 wedge form factor as the 3157 but carries only one filament, meaning the two are not interchangeable despite their physical similarities.
• The 7443 and 7444 are both dual-filament T20 wedge bulbs rated at 12V with a 21W high filament and 5W low filament. Though their electrical characteristics are nearly identical, they are listed as separate part numbers and should not be assumed to be interchangeable without confirming fitment.
• The 1156 differs from all other bulb types in these specifications by using a BA15s bayonet base rather than a wedge base. It is a single-filament bulb rated at 12V and 21W, making it physically incompatible with any wedge-base socket.
• For the 2017-2019 Sierra 3500 HD, the outer tail light bulb depends on whether the truck is equipped with the Chassis Cab package (ZW9). Trucks with ZW9 use the single-filament 1156, while those without ZW9 use the dual-filament 7443.
• The 2014 Sierra splits outer tail light fitment by trim level: the 1500 uses the 7444, while the 3500 HD uses the 3047, a T25 single-filament wedge bulb with a higher wattage output than the T20-based 7444.
• For the 2017-2018 Sierra 1500, the 7443 outer tail light bulb applies only to configurations without the Appearance Package. The 2018 model further specifies this exclusion with the notation "Except GAT," referring to a specific option code.
• The shift from the 3047 to the 7444 on the Sierra 1500 occurred at the 2014 model year, representing a change from a single-filament T25 wedge to a dual-filament T20 wedge with lower overall wattage.
• All bulb types listed in these specifications conform to ANSI standards applicable in both the United States and Canada, indicating standardized sizing and electrical ratings across the North American market.