GMC K1500 Suburban Back Up Light Bulb Size

The GMC K1500 Suburban back up light utilizes bulb sizes 1156, 2356, 2456, 3156, and P21W. Data for the specific components covers the range from 1979 through 1999.

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
1999	2456
1998	3156
1994-1997	2456
1993	2356
1992	2456
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). Dual-filament bulb with BAY15d bayonet base. 12V.	2356
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. 12V, 21W.	1156

Other Locations

Additional Notes

The back up light bulb specifications for the GMC K1500 Suburban span model years 1979 through 1999, with four distinct bulb sizes appearing across that range: 1156, 2356, 2456, and 3156.
The 2456 is the most frequently specified bulb across the listed model years, covering 1992 and 1994-1997, as well as 1999. It is an ANSI-standard festoon bulb rated at 12V and classified as a specialty application type.
The 1156 is the second most common bulb in these specifications, covering model years 1979-1982 and 1984-1986. It is a single-filament bulb with a BA15s bayonet base, rated at 12V and 27W.
Although the 2456 and 1156 are both 12V single-filament bulbs, they use fundamentally different base types. The 1156 uses a BA15s bayonet base, while the 2456 is a festoon-style bulb, meaning the two are not interchangeable.
The 1998 GMC K1500 Suburban is the only model year in these specifications to use the 3156 bulb. The 3156 is a single-filament wedge bulb in a T25 form factor, rated at 12V and 27W.
The 1993 model year is the only one in these specifications to use the 2356 bulb. Unlike all other bulbs listed, the 2356 is a dual-filament type with a BAY15d bayonet base, rated at 12V.
The dual-filament design of the 2356 distinguishes it from every other bulb in these specifications. A BAY15d base has two offset pins to prevent incorrect installation of a dual-filament bulb in a single-filament socket.
The 3156 wedge base and the 1156 BA15s bayonet base are both single-filament 12V bulbs but are physically incompatible due to their different base designs, making substitution between them impossible without a socket adapter.
All four bulb sizes listed across these specifications conform to ANSI standards applicable in both the United States and Canada, indicating standardized electrical and dimensional ratings within those markets.
The 1987-1991 model years are not present in these specifications, and the 1983 year entry lists the 1156 bulb, consistent with the surrounding years in the early 1980s portion of the data.