Mercedes-Benz 500SEL Back Up Light Bulb Size

The Mercedes-Benz 500SEL back up light requires a P21W bulb size for proper installation and function. Data for the specified component covers the range from 1984 through 1993.

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
1992-1993	P21W
1984-1985	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 bulb type listed across all model years of the Mercedes-Benz 500SEL back up light specifications.
The P21W operates on a 12-volt circuit and draws 21 watts, placing it in the standard single-filament signalling category.
The P21W uses a BA15s bayonet base, which is a single-contact bayonet fitting with a 15mm collar width.
As a single-filament bulb, the P21W serves one dedicated function per housing, consistent with its use in a back up light application.
The P21W is governed by ECE standards, reflecting a European and internationally adopted specification rather than a SAE or North American standard.
The Mercedes-Benz 500SEL uses the P21W for the 1984-1985 and 1992-1993 model years in the back up light position.
The BA15s base designation indicates a non-indexed bayonet mount, meaning the bulb has no alignment pin and can be inserted in any rotational orientation, which is appropriate for a single-filament application where polarity of the filament position is not critical.