GMC C3500 Back Up Light Bulb Size

The GMC C3500 back up light utilizes bulb sizes 2456, 3156, 1156, P21W, and 2356 depending on the specific version of the vehicle. Available data for the components spans a range from 1979 through 2000.

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
2000	2456
1999	3156
1998	2456
1993-1997	1156
1992	2356
1990-1991	2456
1988-1989	1156
1979-1986	1156

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
ANSI standard (US & Canada). Dual-filament bulb with BAY15d bayonet base. 12V.	2356

Other Locations

Additional Notes

The 1156 bulb is the most frequently specified back up light bulb across the GMC C3500 model range, appearing in the 1979-1989 and 1993-1997 model years.
The 1156 is a single-filament bulb with a BA15s bayonet base, rated at 12V and 21W, and conforms to ANSI standards for the US and Canadian markets.
The 2456 bulb is specified for the 1990, 1991, 1998, and 2000 model years. It is a festoon-style bulb rated at 12V and designated for specialty applications under ANSI standards.
The 2356 bulb is specified for the 1992 GMC C3500. It is a dual-filament bulb with a BAY15d bayonet base, rated at 12V, and meets ANSI standards for the US and Canadian markets.
The 3156 bulb is specified exclusively for the 1999 model year. It is a single-filament wedge bulb in a T25 form factor, rated at 12V and 27W, conforming to ANSI standards.
The BA15s base of the 1156 and the BAY15d base of the 2356 are physically similar but not interchangeable. The BAY15d base has offset pins to prevent incorrect installation of a dual-filament bulb in a single-filament socket.
The 2456 festoon bulb differs in physical form from the bayonet-base and wedge-base bulbs also specified across this model range, making cross-substitution between these types incompatible without a socket adapter.
The 3156 wedge base and the 1156 bayonet base are not interchangeable, as they use entirely different socket designs despite both being single-filament 12V bulbs.
Four distinct bulb types are specified across the production span of the GMC C3500 for the back up light position, indicating that the same socket configuration was not retained throughout the vehicle's production history.
All four bulb types specified for the GMC C3500 back up lights conform to ANSI standards applicable to both the United States and Canada.