The Ford L8000F front and rear turn signal bulbs utilize 1157 and 1156 sizes. The replacement chart covers 1987 to 1997 production years 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 Ford L8000F front turn signal uses the 1157 bulb for the 1992-1997 model years, as well as for 1987-1989.
The 1157 is a dual-filament bulb operating at 12V with a 21W/5W output and a BAY15d bayonet base, conforming to ANSI standards recognized in both the US and Canada.
The 1156 is a single-filament bulb operating at 12V with a 21W output and a BA15s bayonet base, also conforming to ANSI standards recognized in both the US and Canada.
The BAY15d base of the 1157 and the BA15s base of the 1156 are physically incompatible with each other, meaning the two bulb types are not interchangeable despite sharing the same 15mm bayonet pin spacing.
The Ford L8000F (1991) front turn signal fitment depends on headlamp configuration: the 2-round-headlamp variant takes a 1157, while the 4-rectangular-headlamp variant takes a 1156.
The 1990 model year presents the reverse pairing from 1991, with the 2-round-headlamp configuration requiring a 1156 and the 4-rectangular-headlamp configuration requiring a 1157 for the front turn signal.
The rear turn signal specification varies across model years, with the 1157 dual-filament bulb specified for 1989, 1991, 1992, 1995, and the 1156 single-filament bulb specified for 1987, 1988, 1990, 1993, 1994, 1996, and 1997.
The use of a dual-filament 1157 in certain rear turn signal positions indicates those housings are wired to serve a combined turn and brake light function, as the second filament supports a separate steady-on circuit.
A single-filament 1156 in a rear turn signal position indicates that housing is dedicated solely to the turn signal function, with no shared brake light circuit through that bulb.
Installing a single-filament 1156 in a socket designed for the dual-filament 1157 would result in the loss of one lighting function, as the second filament circuit would remain unserved.