The Subaru DL Brake utilizes 1157 and P21W bulb sizes for the lighting components located at the rear of the vehicle. Available data covers the specific range from 1975 through 1989 for the listed automotive equipment.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Subaru DL brake light specifications cover model years 1975 through 1989, with the 1157 bulb appearing as the predominant fitment across the majority of those years.
The 1157 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. Its dual-filament design allows a single bulb to serve both brake and tail light functions simultaneously.
The P21W follows the ECE standard and carries a single filament rated at 12V and 21W, seated in a BA15s bayonet base. Because it has only one filament, it is dedicated to a single lighting function rather than serving a combined role.
The BAY15d base used by the 1157 and the BA15s base used by the P21W are physically distinct and electrically incompatible. The offset pins on the BAY15d prevent a P21W from seating correctly in a socket designed for the 1157, and vice versa.
For the Subaru DL tail/brake light position, the 1157 is specified for 1976-1979 and 1982-1989, while the P21W is specified for 1975, 1980, and 1981, reflecting a non-continuous alternation between the two standards across the model's production span.
The center high mount stop light (CHMSL) position on the Subaru DL, present for model years 1985-1989, exclusively uses the P21W bulb, making it the sole application where the P21W appears in consecutive years without interruption.
The CHMSL is a separate third brake light mounted higher than the primary brake lights. Its exclusive use of the P21W in the Subaru DL means that vehicles from 1985-1989 require two different bulb types to service all brake light positions on the same car.
Because the 1157 and P21W share the same 21W rating on their primary or sole filament, their light output at full brightness is equivalent, though the 1157 also draws 5W through its secondary filament when operating in tail light mode.