White/GMC WCM Back Up Light Bulb Size

The White/GMC WCM back up light utilizes a 1156 bulb size for illumination purposes within the rear housing assembly. Provided data covers a specific range from 1988 through 1994 for the specified vehicle application.

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
1988-1994	1156

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. 12V, 21W.	1156

Other Locations

Additional Notes

The 1156 is the sole back up light bulb size listed for the White/GMC WCM across the 1988-1994 model years.
The 1156 is an ANSI-standardized bulb type, meaning its physical and electrical specifications conform to a defined industry standard recognized in both the United States and Canada.
The 1156 operates on a 12-volt electrical system and draws 21 watts, which is typical for incandescent automotive signal and reverse lighting applications.
The bulb uses a BA15s bayonet base, a single-contact fitting where the "s" denotes a single pin, distinguishing it from the dual-contact BA15d variant used in other applications.
Because the 1156 is single-filament, it serves one lighting function per socket, which is consistent with its role as a dedicated back up light bulb rather than a combined stop/tail unit.
The BA15s base type is not interchangeable with visually similar bayonet bases that carry two offset pins, such as the BAY15d, despite sharing the same 15mm base width.