GMC C1500 Back Up Light Bulb Size

The GMC C1500 back up light utilizes 1156, 2456, 3156, and P21W bulb sizes depending on the specific version of the vehicle. Available data covers the range from 1979 through 1999 for the components listed in the provided chart.

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

Bulb Specifications

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

Other Locations

Additional Notes

The GMC C1500 back up light specifications span model years 1979 through 1999, with three distinct bulb types used across that range: the 1156, 2456, and 3156.
The 1156 is the most frequently specified bulb across the GMC C1500 back up light fitments, appearing in model years 1979-1986, 1988-1989, and 1993-1997.
The 1156 is a single-filament bulb rated at 12V and 21W, fitted with a BA15s bayonet base, and is recognized under the ANSI standard for the US and Canadian markets.
The BA15s bayonet base on the 1156 is a single-contact bayonet mount, which is not interchangeable with dual-contact bayonet bases used on other automotive bulb types.
The 3156 is a single-filament wedge bulb of the T25 type, rated at 12V and 27W, and is specified for the GMC C1500 in model years 1990 and 1999.
The 3156 operates at a higher wattage than the 1156, and the two bulbs use physically different base types, making them non-interchangeable despite both being single-filament 12V bulbs.
The 2456 is a festoon-type bulb rated at 12V and is designated for specialty applications, appearing in the C1500 specifications for model years 1991-1992 and 1998.
Festoon bulbs such as the 2456 are held in place by contact pressure at each end rather than a base socket, which is a fundamentally different mounting method from both the 1156 and 3156.
All three bulb types specified for the GMC C1500 back up lights conform to ANSI standards applicable to the US and Canadian markets.
Because the 1156, 2456, and 3156 each use a different base or mounting configuration, none of the three bulb types is a direct physical substitute for another, and year-specific fitment must be observed.