BMW 533i Back Up Light Bulb Size

The BMW 533i back up light requires a bulb with the unique size P21W for proper installation. Data for the specific component covers the range from 1983 to 1984.

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
1983-1984	P21W

Bulb Specifications

Description	Bulb Size
ECE standard (Europe & worldwide). Single-filament signalling bulb with BA15s bayonet base. 12V, 21W.	P21W

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Additional Notes

The P21W is the specified back up light bulb for the BMW 533i across the 1983-1984 model years.
The P21W is an ECE-standard bulb, meaning it conforms to the Economic Commission for Europe regulatory framework used in European and worldwide automotive lighting applications.
The P21W operates on a 12-volt electrical system and draws 21 watts, which is typical for single-filament incandescent signalling applications.
As a single-filament bulb, the P21W serves one dedicated lighting function, which in this fitment is the back up light circuit.
The P21W uses a BA15s bayonet base, a single-contact bayonet mount that is not interchangeable with dual-contact bayonet bases such as the BA15d, despite sharing the same 15mm collar size.