Porsche 924 Back Up Light Bulb Size

The Porsche 924 back up light utilizes a P21W bulb size for illumination purposes. Available data for the specified component spans the period from 1977 through 1988.

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
1987-1988	P21W
1977-1982	P21W

Bulb Specifications

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

Other Locations

Additional Notes

The P21W is the sole bulb type specified for the Porsche 924 backup light across all listed model years.
The P21W is an ECE-standard single-filament bulb rated at 12 volts and 21 watts, designed primarily for signalling applications such as reverse lights.
The P21W uses a BA15s bayonet base, which is a single-contact bayonet fitting with a 15mm collar width.
The BA15s base designation indicates a single-contact configuration, distinguishing it from the dual-contact BA15d variant, which is not interchangeable with the P21W.
The Porsche 924 (1977-1982) and the 1987-1988 model years all share the same P21W backup light bulb specification.
The ECE designation on the P21W reflects compliance with United Nations Economic Commission for Europe lighting regulations, a standard adopted across European and many international markets.
Because the P21W is a single-filament bulb, it serves one lighting function only and is not suited for combined stop and tail applications, which require dual-filament alternatives.