International S1723 front turn signal bulbs measure 1156 in size, while rear turn signal bulbs measure 1157 in size. The replacement chart covers bulb specifications across 1980 to 1985 vehicle production years.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The International S1723 uses the 1156 bulb for the front turn signal across all listed model years, 1980-1985.
The 1156 is an ANSI-standard single-filament bulb rated at 12V and 21W, fitted with a BA15s bayonet base.
The rear turn signal on the International S1723 uses the 1157 bulb across the same 1980-1985 model year range.
The 1157 is an ANSI-standard dual-filament bulb rated at 12V with a 21W/5W output, fitted with a BAY15d bayonet base.
The front and rear turn signals require different bulb types. The 1156 and 1157 are not interchangeable, as their bayonet bases differ: BA15s for the 1156 and BAY15d for the 1157.
The BAY15d base of the 1157 features offset pins that prevent incorrect installation of a single-filament bulb in a dual-filament socket, making physical substitution with the 1156 mechanically incompatible.
Both the 1156 and 1157 conform to ANSI standards recognized in the United States and Canada.
The dual-filament 1157 serves the rear position because it supports two brightness levels, with the lower 5W filament typically used for a running or parking light function alongside the higher 21W turn signal filament.