Audi Coupe front turn signal bulbs use P21/5W size while rear turn signal bulbs use P21W size. The replacement chart covers 1981 to 1987 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 Audi Coupe uses two distinct bulb types across its front and rear turn signal positions for the 1981-1987 model years: the P21/5W at the front and the P21W at the rear.
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 P21W is a single-filament bulb rated at 12V at 21W, mounted on a BA15s bayonet base.
Both bulb types conform to ECE standards, indicating they are specified for European and worldwide markets rather than SAE-regulated North American applications.
The BAY15d base of the P21/5W and the BA15s base of the P21W are not interchangeable, as the BAY15d features offset pins to accommodate its dual-filament design, while the BA15s uses a single-pin configuration suited to a single filament.
Because the Audi Coupe (1981-1987) front turn signal position calls for the dual-filament P21/5W, substituting a single-filament P21W in that position would be incorrect regardless of the shared 21W output rating.
The front turn signal position of the Audi Coupe specifies the P21/5W across all seven model years covered, indicating no change in the front turn signal bulb requirement throughout that production span.
The rear turn signal position similarly specifies the P21W without variation across the full 1981-1987 range.