Mazda RX-3 Back Up Light Bulb Size

The Mazda RX-3 back up light uses 1156 and P21W bulb sizes according to the provided specifications for the vehicle. Data for the bulb sizes covers the range from 1972 to 1978.

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
1972-1978	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 Mazda RX-3 uses the 1156 bulb across all listed model years, spanning 1972-1978, for the back up light position.
The 1156 is an ANSI-standardized bulb type, meaning its physical and electrical specifications conform to a defined North American standard used across the automotive industry in the United States and Canada.
The 1156 operates on a 12-volt electrical system and draws 21 watts, which is typical of incandescent single-filament automotive bulbs intended for signaling and reversing light applications.
The 1156 uses a BA15s bayonet base, where "BA15s" denotes a single-contact bayonet fitting with a 15mm base width. The single-contact design corresponds directly to the single-filament construction of the bulb.
Because the 1156 is a single-filament bulb, it serves one dedicated function per socket. This distinguishes it from dual-filament variants such as the 1157, which would not be a compatible substitute in a single-filament application.