Acura Legend front turn signal bulbs utilize 1157NA size while rear turn signal bulbs use P21W size. The replacement chart covers 1986 to 1988 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 Acura Legend uses two distinct bulb standards across its front and rear turn signal positions, reflecting a split between North American and European lighting specifications within the same vehicle.
The 1157NA is an ANSI-standard dual-filament bulb rated 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 simultaneously.
The natural amber glass of the 1157NA produces its amber signal color directly from the envelope rather than from a colored lens, which distinguishes it from the clear-glass 1157 variant used in applications where the housing itself provides the color.
The BAY15d base of the 1157NA features two offset pins at different heights, a design that prevents incorrect insertion and ensures the two filaments are connected to the correct circuits.
The P21W is an ECE-standard single-filament bulb rated at 12V and 21W, mounted on a BA15s bayonet base. Its single filament means it is dedicated solely to the turn signal function rather than shared with a parking light circuit.
The BA15s base of the P21W has a single pin, which physically distinguishes it from the dual-pin BAY15d base of the 1157NA. The two base types are not interchangeable despite sharing a similar 15mm collar size.
The front turn signal position on the Acura Legend (1986-1988) uses the 1157NA across all three model years, while the rear turn signal position uses the P21W across the same span.
Because the 1157NA and P21W share the same 21W output on their primary filaments but differ in base configuration and filament count, substituting one for the other is not possible without a socket adapter or wiring modification.