The BMW 525i brake light requires a P21W bulb size for proper operation and visibility on the road. Available data for the specified component covers the period from 1989 to 2007.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The BMW 525i uses the P21W bulb type across all listed brake light positions, covering model years 1989-2007 for the standard brake light and 1989-1995 plus 2001-2003 for the Center High Mount Stop Light.
The P21W is an ECE-standardized bulb, meaning it conforms to European and internationally recognized regulations for automotive lighting components.
P21W bulbs operate at 12 volts with a 21-watt output, which is a common rating for single-filament stop and signal applications in passenger vehicles.
The P21W uses a BA15s bayonet base, a single-contact fitting where the "s" denotes a single pin offset to one side, which prevents incorrect installation orientation.
Because the P21W is single-filament, it serves a dedicated function such as braking, rather than a combined stop and tail function, which would require a dual-filament bulb such as the P21/5W.
The BA15s bayonet base of the P21W is not interchangeable with the BAY15d base found on dual-filament variants, as the pin positions differ between the two base types.
The consistent use of P21W across the BMW 525i's listed brake light positions means the same bulb specification applies to both the standard brake lights and the Center High Mount Stop Light on applicable model years.