White/GMC WCS Back Up Light Bulb Size

The White/GMC WCS back up light requires a 1156 bulb size for proper installation and function. Data for the specific component covers the period from 1988 through 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
1988-1991	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 White/GMC WCS uses the 1156 bulb for the back up light across the 1988-1991 model years.
The 1156 is an ANSI-standardized bulb type recognized in both the United States and Canada.
It operates on a 12-volt electrical system and draws 21 watts.
The 1156 is a single-filament bulb, meaning it serves one lighting function rather than combining two, such as stop and tail.
It uses a BA15s bayonet base, which is a single-contact bayonet mount that locks into the socket with a twist.
The BA15s base is not interchangeable with the BA15d base, which features two contact pins rather than one, so substitution between the two base types is not compatible.