Kenworth C540 front turn signal bulbs measure 1157 in size, while rear turn signal bulbs measure 1156 in size. The replacement chart covers vehicle production spanning 1985 to 1993 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 Kenworth C540 uses the 1157 bulb for the front turn signal across the 1985, 1992, and 1993 model years.
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 BAY15d base features offset pins, which physically prevents it from being interchanged with single-filament bulbs that use a different base configuration.
The rear turn signal on the Kenworth C540 uses the 1156 bulb for the same model years covered in the specifications.
The 1156 is a single-filament bulb rated at 12V and 21W, fitted with a BA15s bayonet base.
The BA15s base uses a single contact pin, making it mechanically incompatible with the BAY15d socket used by the 1157 at the front position.
Both the 1157 and 1156 are ANSI-standardized bulbs recognized in the United States and Canada, meaning their electrical and physical specifications conform to a defined industry standard.
Although the 1157 and 1156 share the same 21W output on their primary filaments, the dual-filament design of the 1157 serves a combined turn signal and parking light function, while the single-filament 1156 serves a dedicated turn signal function at the rear.