The Autocar DK front turn signal bulb size is P21W, while rear turn signal bulbs measure 1157 and 198 in size. The replacement chart covers vehicle production years spanning 1983 to 1988.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Autocar DK front turn signal uses the P21W bulb across the 1983-1988 model years. This is an ECE-standard single-filament bulb rated at 12V and 21W, fitted with a BA15s bayonet base.
The BA15s base of the P21W is a single-contact bayonet mount. Its single-filament design means it serves one lighting function only, which is consistent with dedicated turn signal applications.
The Autocar DK rear turn signal uses the 1157 bulb for the 1985-1988 model years. This is an ANSI-standard dual-filament bulb rated at 12V with filaments drawing 21W and 5W respectively, fitted with a BAY15d bayonet base.
The BAY15d base of the 1157 is a dual-contact bayonet mount. The offset pins of the BAY15d prevent incorrect insertion, as each pin position corresponds to a separate filament circuit.
The Autocar DK rear turn signal uses the 198 bulb for the 1983-1984 model years. This is an ANSI-standard miniature wedge bulb in a T5 form factor, rated at 12V and 2W.
The rear turn signal specification changed between the 1984 and 1985 model years, shifting from the 198 wedge bulb to the 1157 dual-filament bayonet bulb. These two types use physically incompatible bases and are not interchangeable.
The front P21W and the rear 1157 share the same 12V, 21W output rating for their primary filaments, but their bases differ. The BA15s of the P21W and the BAY15d of the 1157 are distinct bayonet types and cannot be substituted for one another.
The 198 bulb, used in the 1983-1984 rear turn signal, operates at only 2W, which is substantially lower than the 21W output of both the P21W and the primary filament of the 1157. This difference reflects a distinct circuit and socket design for those model years.
The P21W follows ECE regulations, while both the 1157 and the 198 follow ANSI standards. These two regulatory frameworks define different testing and performance criteria, and bulbs certified under one standard are not rated as equivalent to those under the other.
The front turn signal socket on the Autocar DK is designed for the BA15s bayonet base throughout the 1983-1988 model years, as the P21W specification remains unchanged across all six years.