The International S1853FC front turn signal requires a 1156 bulb size while the rear turn signal uses a 1157 bulb size. The replacement chart covers 1987 to 1989 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 International S1853FC uses two distinct bulb types across its turn signal positions: the 1156 for the front and the 1157 for the rear, across the 1987-1989 model years.
The 1156 is a single-filament bulb operating at 12V and 21W, fitted with a BA15s bayonet base, and is classified under the ANSI standard applicable in the US and Canada.
The 1157 is a dual-filament bulb rated at 12V with a primary filament drawing 21W and a secondary filament drawing 5W, fitted with a BAY15d bayonet base, also under the same ANSI standard.
The BA15s base of the 1156 and the BAY15d base of the 1157 are not interchangeable. The BAY15d base features offset locating pins that prevent a single-filament 1156 from seating correctly in a dual-filament socket.
The dual-filament design of the 1157 allows the rear turn signal socket to serve two brightness levels, with the higher 21W filament typically assigned to the turn signal function and the lower 5W filament to a secondary function such as a running or parking light.
The single-filament 1156 in the front turn signal position operates at a fixed 21W output, as no secondary filament is present to support an alternate brightness level.
Both the 1156 and 1157 share the same 12V operating voltage, which is consistent with the standard electrical system voltage found in commercial vehicles of this type.
The fitment of the 1156 (International S1853FC front turn signal) remains consistent across all three listed model years, indicating no front socket design change occurred within the 1987-1989 production span.
The rear turn signal fitment of the 1157 is likewise unchanged across the 1987-1989 model years, reflecting a stable rear lamp socket specification throughout that period.