Porsche 924 front turn signal bulbs use P21/5W size while rear turn signal bulbs use P21W size. The replacement chart covers 1977 through 1988 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 Porsche 924 front turn signal uses the P21/5W bulb across all listed model years from 1977-1982 and 1987-1988.
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, which physically prevents incorrect single-filament bulbs from being seated in a dual-filament socket.
The Porsche 924 rear turn signal uses the P21W bulb across all listed model years from 1977-1982 and 1987-1988.
The P21W is a single-filament bulb rated at 12V at 21W, mounted on a BA15s bayonet base with symmetrically placed pins.
The front and rear turn signal bulbs on the 924 are not interchangeable, as the P21/5W uses a BAY15d base and the P21W uses a BA15s base, making them physically incompatible with each other's sockets.
Both the P21/5W and P21W conform to ECE standards, a regulatory framework recognized across Europe and numerous other markets worldwide.
Despite sharing the same 21W turn signal filament output, the P21/5W and P21W serve distinct functions due to the dual-filament design of the former, which supports a secondary 5W circuit alongside the primary signalling filament.