GMC Caballero Back Up Light Bulb Size

The GMC Caballero back up light uses 1156 and P21W bulb sizes for the rear illumination components. Data for the specific lighting requirements covers the period from 1978 to 1987.

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
1978-1987	1156

Bulb Specifications

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

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Additional Notes

The GMC Caballero uses the 1156 bulb size for the back up light across the 1978-1987 model years.
The 1156 is an ANSI-standardized bulb type, meaning its specifications are governed by a recognized North American standard applicable in both the United States and Canada.
The 1156 bulb operates on a 12-volt electrical system and draws 21 watts, which is consistent with standard automotive reverse lighting applications.
The 1156 is a single-filament bulb, meaning it serves one lighting function rather than combining two, such as stop and tail duties.
The 1156 uses a BA15s bayonet base, where "BA15s" denotes a bayonet-style mount with a 15mm base width and a single contact pin at the base.
The BA15s single-contact bayonet base is not interchangeable with the BA15d base, which carries two offset contact pins and is used on dual-filament bulbs such as the 1157.