GMC C3500HD Back Up Light Bulb Size

The GMC C3500HD back up light utilizes bulb sizes 2456, 3156, and 1156 depending on the specific version of the vehicle. Provided information covers a range from 1991 through 2002 for the listed components.

The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.

Bulb Size by Year Range

Years	Bulb Size
2001-2002	2456
1998-2000	3156
1993-1997	1156
1991-1992	3156 (Medium Duty)

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Festoon bulb, specialty application. 12V.	2456
ANSI standard (US & Canada). Single-filament wedge bulb (T25). 12V, 27W.	3156
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. 12V, 21W.	1156

Other Locations

Additional Notes

The GMC C3500HD backup light specifications cover model years 1991 through 2002, with three distinct bulb types used across that span: the 2456, 3156, and 1156.
The 1156 is the most frequently specified bulb in these records, covering the GMC C3500HD from 1993 through 1997. It is a single-filament bulb rated at 12V and 21W, fitted with a BA15s bayonet base.
The BA15s bayonet base on the 1156 uses a single contact pin, which is not interchangeable with dual-pin bayonet bases found on other automotive bulb types.
The 3156 appears across multiple non-consecutive year groups in these specifications. It is a single-filament wedge bulb in the T25 form factor, rated at 12V and 27W, and draws more wattage than the 1156.
For 1991-1992, the 3156 specification carries a Medium Duty designation, indicating that fitment applies specifically to the medium duty configuration of the C3500HD in those years.
The T25 wedge base of the 3156 is a push-in style connector, which is physically incompatible with the BA15s bayonet base of the 1156. The two bulb types are not interchangeable despite both being single-filament 12V bulbs.
The 2456 is specified for the 2001-2002 model years. It is classified as a festoon bulb intended for specialty applications and operates at 12V under the ANSI standard for the US and Canada.
A festoon bulb such as the 2456 uses end-cap contacts rather than a base socket, making it physically distinct from both the wedge and bayonet base types used in earlier C3500HD model years.
All three bulb types in these specifications, the 2456, 3156, and 1156, conform to ANSI standards applicable in the US and Canada.
The backup light bulb specification changed three times across the recorded model years of the C3500HD, shifting from the 1156 to the 3156 between 1997 and 1998, and then from the 3156 to the 2456 between 2000 and 2001.