Porsche 928 Back Up Light Bulb Size

The Porsche 928 back up light utilizes a P21W bulb size for illumination purposes. Available data for the specified component covers the range from 1978 through 1995.

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
1993-1995	P21W
1978-1991	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 Porsche 928 uses the P21W bulb for the back up light across all model years from 1978 to 1995, with the sole exception of 1992.
The P21W is an ECE-standard single-filament bulb rated at 12 volts and 21 watts, designed for signalling applications such as reverse lighting.
P21W bulbs use a BA15s bayonet base, which is a single-contact bayonet fitting with a 15mm collar.
The BA15s base is distinct from the BA15d double-contact bayonet base; the two are not interchangeable despite sharing the same collar size.
The ECE designation on the P21W indicates the bulb conforms to United Nations Economic Commission for Europe regulations, a standard widely adopted outside North America.
At 21 watts, the P21W produces a relatively high output for a single-filament signal bulb, which is consistent with its use in reverse lighting where broad illumination of the area behind the vehicle is required.