Ford Bronco II front turn signal bulbs measure 3157 or 1157 in size, while rear turn signal bulbs measure 1157 in size. The replacement chart covers 1984 to 1990 model 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 Bronco II uses two distinct bulb types across its front turn signal positions: the 1157 for model years 1984-1987 and the 3157 for model years 1988-1990.
The rear turn signal position uses the 1157 bulb across all model years covered by these specifications, from 1984 through 1990.
Both the 1157 and 3157 are dual-filament bulbs, meaning each contains two separate filaments within a single housing to serve two lighting functions, typically a brighter output for signaling and a dimmer output for running or parking light duty.
The 3157 is a T25 wedge-type bulb, which uses a plastic wedge base that friction-fits directly into the socket without a separate locking mechanism.
The 1157 uses a BAY15d bayonet base, a two-pin offset base that locks into the socket with a twist. The offset pin placement is a deliberate design feature that prevents incorrect insertion orientation.
The 3157 operates at 12 volts with a wattage rating of 27W on its high-intensity filament and 7W on its low-intensity filament.
The 1157 operates at 12 volts with a wattage rating of 21W on its high-intensity filament and 5W on its low-intensity filament.
The 3157 and 1157 are not interchangeable. Their base types differ fundamentally, with the wedge base of the 3157 being physically incompatible with the bayonet socket designed for the 1157.
Both bulb types conform to ANSI standards applicable in the United States and Canada, indicating standardized electrical and physical tolerances across manufacturers producing these part numbers.
The front turn signal position of the Ford Bronco II reflects a mid-production change in bulb specification, shifting from the BAY15d-based 1157 to the wedge-based 3157 between the 1987 and 1988 model years.