Kenworth T800 front turn signal bulbs use 1157 size while rear turn signal bulbs use 1156 or 1157 size. The replacement chart covers vehicle production spanning 1987 to 1997 with corresponding bulb specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Kenworth T800 front turn signal uses the 1157 bulb across all listed model years from 1987-1997.
The 1157 is a dual-filament bulb operating at 12 volts with a 21W/5W output rating, meaning it carries two separate filaments within a single envelope, each serving a distinct function at different wattages.
The 1157 bulb uses a BAY15d bayonet base, a two-pin offset base design that prevents incorrect installation by ensuring only one rotational orientation fits the socket.
The rear turn signal on the T800 uses the 1156 bulb for 1987-1990 and 1992-1997, while the 1991 model year uses the 1157 instead.
The 1156 is a single-filament bulb rated at 12 volts and 21W, making it electrically distinct from the dual-filament 1157 despite sharing the same voltage rating and primary wattage.
The 1156 uses a BA15s bayonet base, which is a single-pin design. Although the 1156 and 1157 share a similar physical profile, their base configurations differ, and the two bulbs are not interchangeable.
Both the 1156 and 1157 are ANSI-standardized bulbs recognized in the United States and Canada, meaning their electrical and physical specifications conform to a defined industry standard rather than a proprietary format.
The 1991 T800 rear turn signal socket accepts the 1157 with its BAY15d two-pin base, which is mechanically incompatible with the BA15s single-pin socket used in surrounding model years, making direct substitution between the two bulb types inadvisable without confirming the socket type.