BMW 735i front turn signal bulbs use a P21/5W size while rear turn signal bulbs require a P21W size. The replacement chart covers 1985 to 1992 model 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 735i uses the P21/5W bulb for the front turn signal across the 1985-1992 model years.
The P21/5W is a dual-filament bulb rated at 12V with a 21W primary filament and a 5W secondary filament, mounted on a BAY15d bayonet base. The dual-filament design allows a single bulb to serve two lighting functions simultaneously.
The BAY15d base features two offset pins at different heights, which physically prevents incorrect installation of a single-filament bulb in a socket intended for a dual-filament application.
The rear turn signal on the BMW 735i uses the P21W bulb across the 1985-1992 model years.
The P21W is a single-filament bulb rated at 12V and 21W, fitted with a BA15s bayonet base. The BA15s base has a single pin and is not interchangeable with the BAY15d base used by the P21/5W.
Because the front and rear turn signals use different base types, BAY15d and BA15s respectively, the two bulbs are not interchangeable with each other despite sharing the same 21W turn signal filament output.
Both the P21/5W and P21W conform to ECE standards, a regulatory framework recognized across Europe and numerous other markets worldwide.