Chevrolet K5 Blazer Back Up Light Bulb Size

The Chevrolet K5 Blazer back up light utilizes 1156 and P21W bulb sizes for illumination. Data for the specific components covers the range from 1975 through 1986.

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
1975-1986	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 Chevrolet K5 Blazer uses the 1156 bulb for its back up light across the 1975-1986 model years.
The 1156 is an ANSI-standardized bulb type, meaning its physical and electrical specifications are defined by a recognized industry standard shared across the United States and Canada.
The 1156 operates on a 12-volt electrical system and draws 21 watts, which is consistent with standard automotive reverse lighting applications.
The bulb uses a BA15s bayonet base, a single-contact mount where the "s" denotes a single pin, distinguishing it from the dual-contact BA15d variant.
The 1156 is a single-filament bulb, meaning it serves one lighting function only, which in this application is the back up light.
Because the BA15s base is a single-contact design, it is not interchangeable with visually similar bayonet bulbs that carry two contact pins, such as the 1157, despite sharing the same base collar width.