International S1724 front turn signal bulbs use 1156 size while rear turn signal bulbs use 1157 size. The replacement chart covers vehicle production spanning 1980 to 1984.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The International S1724 uses the 1156 bulb for the front turn signal and the 1157 bulb for the rear turn signal across the 1980-1984 model years.
The 1156 is a single-filament bulb rated at 12V and 21W, built to ANSI standards applicable in both the United States and Canada.
Its base type is BA15s, a single-contact bayonet fitting where the single contact pin is centered on the base.
The 1157 is a dual-filament bulb sharing the same 12V operating voltage, with filaments rated at 21W and 5W respectively, also conforming to ANSI standards for the US and Canadian markets.
The 1157 uses a BAY15d bayonet base, which features two offset contact pins to prevent incorrect installation and to distinguish it from single-filament bayonet bases.
The dual-filament design of the 1157 allows the rear turn signal to serve more than one lighting function, with the lower-wattage filament typically dedicated to a secondary role such as a running or parking light.
Although the 1156 and 1157 share a similar physical profile and both use bayonet-style bases, their base configurations are not interchangeable due to the difference between BA15s and BAY15d pin arrangements.
The consistent use of the same bulb type across all five model years for each position indicates no mid-cycle change in lighting hardware for the S1724 during the 1980-1984 period.