Kenworth T680 Turn Signal Bulb Size

Additional Notes

• The 4157NA is an ANSI-standard dual-filament wedge bulb in the T25 form factor, rated at 12V with a 27W high filament and 7W low filament. The "NA" designation indicates natural amber glass, meaning the amber color is produced by the glass itself rather than an applied coating.
• The 5702AK is a Sylvania part number for a coated variant of the ANSI 3157 bulb. It shares the same T25 wedge form factor and 12V, 27W/7W electrical ratings as the 4157NA, but achieves its amber output through a coating applied to the bulb surface rather than through tinted glass.
• Both the 4157NA and 5702AK are dual-filament bulbs, meaning each serves two lighting functions from a single unit. In a front turn signal application, the higher 27W filament typically handles the turn signal flash, while the lower 7W filament handles a secondary function such as a daytime running or parking light.
• The Kenworth T680 front turn signal used the 5702AK exclusively in the 2014 model year, while the 4157NA was specified for the 2013 and 2015 model years.
• Although the 4157NA and 5702AK share the same T25 wedge base and identical voltage and wattage ratings, they are not the same part. The 4157NA is an ANSI-designated bulb, while the 5702AK is a proprietary Sylvania designation referencing a coated 3157 variant. Substituting one for the other may affect color output consistency depending on the lens housing used.