The Ferrari Testarossa front turn signal requires a 1157 bulb size, while the rear turn signal uses either a 1073 or P21W bulb size. The replacement chart covers 1985 to 1989 production years with corresponding bulb size specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Ferrari Testarossa uses the 1157 bulb for the front turn signal across all listed model years, 1985-1989.
The 1157 is a dual-filament bulb operating at 12V with a 21W main filament and a 5W secondary filament, mounted on a BAY15d bayonet base. The dual-filament design allows a single bulb to serve both turn signal and parking light functions.
The BAY15d base features two offset pins at different heights, which prevents incorrect installation and distinguishes it from single-filament bayonet bases.
The rear turn signal of the Ferrari Testarossa uses the P21W bulb for model years 1985-1988.
The 1989 Ferrari Testarossa rear turn signal uses the 1073 bulb, which differs from the P21W used in the four preceding model years.
Both the 1073 and P21W share the BA15s bayonet base, meaning they are physically interchangeable in terms of socket fitment. However, they differ in wattage: the 1073 operates at 13W while the P21W operates at 21W.
The P21W follows the ECE standard, which is used in Europe and internationally, while the 1073 follows the ANSI standard used in the United States and Canada. This distinction reflects differing regional regulatory frameworks for automotive lighting.
The 1073 is a lower-wattage variant of the 1156 bulb. Both share the BA15s base and single-filament construction, but the 1073 draws less power.
Substituting a P21W for a 1073 in the 1989 rear turn signal position would introduce a higher wattage load than the original specification, which may affect compatibility with the vehicle's turn signal flasher relay.