The Ford L8501 front turn signal requires a 1157 bulb size while the rear turn signal uses a 1156 bulb size. The replacement chart covers vehicle production spanning 1997 to 1998.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Ford L8501 uses two distinct bulb types across its turn signal positions: the 1157 at the front and the 1156 at the rear, both for the 1997-1998 model years.
The 1157 is a dual-filament bulb rated at 12V with a 21W/5W output, meaning it carries one filament for the higher-intensity turn signal function and a second for a lower-intensity running or parking light function.
The 1156 is a single-filament bulb rated at 12V and 21W, dedicated solely to one lighting function, which in this application is the rear turn signal.
Both the 1157 and 1156 conform to ANSI standards recognized in the United States and Canada, placing them within a widely adopted North American specification framework.
The 1157 uses a BAY15d bayonet base, which features two offset pins at different heights to ensure correct orientation during installation and to prevent the dual filaments from being connected to the wrong circuits.
The 1156 uses a BA15s bayonet base, a single-contact version with two pins at the same height, reflecting its single-filament design.
Because the 1157 (BAY15d) and 1156 (BA15s) have physically different base configurations, the two bulb types are not interchangeable with each other, even though both share the same 12V operating voltage and a 21W primary filament rating.