Subaru RX Back Up Light Bulb Size

The Subaru RX back up light uses bulb size 1156 or P21W depending on the specific version of the vehicle. Data for the bulb size covers the range from 1985 to 1989.

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
1985-1989	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 bulb type specified for the back up light across all listed model years of the Subaru RX, covering 1985-1989.
The 1156 is a single-filament bulb, meaning it serves one lighting function only, which is consistent with its dedicated use as a back up light.
The bulb operates at 12 volts and 21 watts, placing it within the standard low-voltage automotive electrical range typical of passenger vehicles.
The 1156 uses a BA15s bayonet base, a single-contact fitting where the "s" denotes a single pin, distinguishing it from the dual-contact BA15d variant.
The 1156 designation follows ANSI standards recognized in both the United States and Canada, indicating cross-border fitment consistency under North American automotive norms.
Because the BA15s base is a single-contact design, it is not interchangeable with visually similar bayonet bulbs that carry a dual-contact base, despite sharing the same physical base width.