Audi Coupe Back Up Light Bulb Size

The Audi Coupe back up light requires a P21W bulb size for proper installation and function within the rear lighting assembly. Available data covers the specific range from 1981 through 1987 for the listed vehicle.

The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.

Bulb Size by Year Range

Years	Bulb Size
1981-1987	P21W

Bulb Specifications

Description	Bulb Size
ECE standard (Europe & worldwide). Single-filament signalling bulb with BA15s bayonet base. 12V, 21W.	P21W

Other Locations

Additional Notes

The Audi Coupe uses the P21W bulb for its back up light across the 1981-1987 model years.
The P21W is an ECE-standard bulb, meaning it conforms to the regulatory framework governing lighting equipment in Europe and numerous other markets worldwide.
P21W bulbs operate on a 12-volt electrical system and draw 21 watts, which is typical for single-filament signalling applications.
The single-filament design of the P21W reflects its dedicated signalling function, as opposed to dual-filament bulbs that serve two lighting roles within one unit.
The P21W uses a BA15s bayonet base, where "BA15" denotes the 15mm bayonet cap and "s" indicates a single contact at the base, distinguishing it from the dual-contact BA15d variant.
The BA15s base is not interchangeable with the BA15d base despite sharing the same physical cap width, as the contact configuration differs between the two.