The International S1654LP front turn signal uses a 1156 bulb size while the rear turn signal requires a 1157 bulb size. The replacement chart covers 1988 to 1989 vehicle 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 S1654LP uses two distinct bulb types across its turn signal positions: the 1156 for the front and the 1157 for the rear, covering both the 1988-1989 model years.
The 1156 is a single-filament bulb operating at 12V and 21W, fitted with a BA15s bayonet base, and is recognized under ANSI standards in the US and Canada.
The 1157 is a dual-filament bulb rated at 12V with a 21W primary filament and a 5W secondary filament, mounted on a BAY15d bayonet base, also carrying ANSI recognition in the US and Canada.
The BA15s base of the 1156 and the BAY15d base of the 1157 are not interchangeable. The BAY15d base features offset pins to prevent incorrect installation, while the BA15s base uses a single-contact, symmetrical pin arrangement.
The dual-filament design of the 1157 allows it to serve both turn signal and running light functions simultaneously, which is why it is suited to the rear position on the International S1654LP.
The single-filament 1156 used at the front turn signal position does not carry a secondary running light circuit, distinguishing its function from the rear 1157 application.
Although both bulbs share a 12V operating voltage and a 21W output on their primary filament, the physical base types differ, making one a non-fitting substitute for the other despite the shared wattage rating.