GMC V3500 Back Up Light Bulb Size

The GMC V3500 back up light requires bulb sizes 2456, 2356, P21W, or 1156 depending on the specific application. Data for the bulb sizes covers the range from 1987 to 1991.

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
1991	2456
1990	2356
1987-1989	1156

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Festoon bulb, specialty application. 12V.	2456
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 GMC V3500 back up light bulb specifications span model years 1987 through 1991, covering three distinct bulb types across that period.
The 1156 bulb is the most frequently specified type, appearing in the GMC V3500 across 1987-1989. It is a single-filament bulb rated at 12V and 21W, fitted with a BA15s bayonet base, and meets ANSI standards for the US and Canadian markets.
The BA15s bayonet base on the 1156 uses a single contact pin, which is a defining physical characteristic that distinguishes it from dual-contact bayonet bases used in other bulb types.
The 1990 GMC V3500 uses the 2356 bulb, a dual-filament type with a BAY15d bayonet base, also rated at 12V and conforming to ANSI standards for the US and Canadian markets.
The BAY15d base on the 2356 features two offset pins, a design that physically prevents it from being seated in a BA15s socket, making the 1156 and 2356 non-interchangeable despite both using bayonet-style bases.
The 1991 GMC V3500 uses the 2456 bulb, a festoon-type bulb rated at 12V and designated for specialty applications under ANSI standards for the US and Canadian markets.
A festoon bulb, such as the 2456, is cylindrical in form and mounts by contact pressure at each end rather than through a base socket, making it physically incompatible with the bayonet-base sockets used by the 1156 and 2356.
Because the 1991 model year uses a festoon bulb while the 1990 model uses a dual-filament bayonet bulb, the back up light socket design of the V3500 changed between those two model years, and the bulbs are not interchangeable.