Kenworth T600A front turn signal bulbs use 1157 size while rear turn signal bulbs use 1156 or 1157 size. Replacement chart data covers 1986 to 1997 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 Kenworth T600A front turn signal uses the 1157 bulb across all listed model years from 1986-1997, making it the only bulb type specified for that position throughout the entire documented range.
The 1157 is a dual-filament bulb operating at 12 volts with a 21W/5W output, meaning it carries two separate filaments within a single envelope, each serving a different wattage and function.
The 1157 uses a BAY15d bayonet base, which is an offset two-pin mount. The offset pin placement is a deliberate design feature that prevents incorrect insertion of the bulb into the socket.
The rear turn signal on the T600A does not follow a single consistent bulb type across model years, with the specifications alternating between the 1156 and 1157 depending on the year.
The 1156 is a single-filament bulb rated at 12 volts and 21W, using a BA15s bayonet base. The BA15s base features two pins at equal positions, distinguishing it physically from the BAY15d base of the 1157.
Although the 1156 and 1157 share the same 21W primary filament rating and a similar bayonet base style, they are not interchangeable. The differing base pin offsets and filament counts make substitution between the two a fitment error.
Both the 1156 and 1157 are classified under ANSI standards and are recognized in both the United States and Canada, placing them within a widely distributed and standardized bulb family.
For the rear turn signal, the 1157 is specified for the Kenworth T600A in model years 1986, 1988, 1991, 1994, and 1996, while the 1156 applies to 1987, 1989, 1990, 1992, 1993, 1995, and 1997.