The BMW 325 front turn signal requires a P21/5W bulb size while the rear turn signal uses a P21W bulb size. The replacement chart covers 1986 to 1988 model production years with corresponding bulb specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The BMW 325 uses two distinct ECE-standard bulb types across its front and rear turn signal positions for the 1986-1988 model years.
The P21/5W is a dual-filament bulb rated at 12V with a 21W main filament and a 5W secondary filament, mounted on a BAY15d bayonet base.
The BAY15d base features offset pins, a design that prevents incorrect insertion by ensuring the bulb can only be seated in one orientation.
The P21W is a single-filament bulb rated at 12V and 21W, mounted on a BA15s bayonet base.
The BA15s base uses a single contact at the base tip, distinguishing it from the dual-contact BAY15d used by the P21/5W.
The BMW 325 front turn signal position calls for the P21/5W across the full 1986-1988 span, while the rear turn signal position uses the P21W across the same years.
The P21/5W and P21W are not interchangeable. Their base types differ, and the P21/5W carries a second filament that the P21W does not, making physical and electrical substitution between the two incompatible.
Both bulb types conform to ECE regulations, a standard recognized across Europe and numerous other markets worldwide.