BMW 735i Back Up Light Bulb Size

The BMW 735i back up light utilizes a P21W bulb size for illumination purposes. Available data for the specified component covers the period from 1985 through 1992.

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
1985-1992	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 sole backup light bulb type specified for the BMW 735i across all listed model years, 1985-1992.
The P21W operates at 12 volts with a 21-watt output, placing it in the standard single-filament signaling category.
A single filament means the bulb serves one lighting function only, which is consistent with its role as a dedicated backup light.
The P21W uses a BA15s bayonet base, a single-contact fitting where the "s" denotes a single pin offset to one side, preventing incorrect installation orientation.
This bulb type is governed by ECE (Economic Commission for Europe) standards, giving it broad compatibility across European and worldwide vehicle applications.
The consistent P21W fitment across the entire 1985-1992 production span of the BMW 735i indicates no bulb specification change occurred during that generation.
Because the BA15s base is a single-contact design, it is not interchangeable with the BA15d base, which carries two contacts and is used in dual-filament applications.