2024 Kenworth T680 Bulb Size Chart & Replacement Guide

As an ASE-certified master technician, I know that for heavy-duty drivers, proper lighting isn’t just a matter of convenience—it’s a major safety and DOT compliance issue. The 2024 Kenworth T680, especially the Next Gen models, features some of the most advanced aerodynamic lighting in the commercial trucking industry.

While the new T680 comes standard with sleek, fully integrated LED headlight assemblies, many fleets and owner-operators may still operate trims equipped with traditional halogen setups to reduce initial purchase costs. Knowing your exact bulb sizes and replacement procedures can save you from costly downtime and DOT violations. Below is your comprehensive guide to the 2024 Kenworth T680 lighting system.

Quick reference

Note: The 2024 Kenworth T680 "Next Gen" heavily utilizes sealed, fully integrated LED assemblies. If your truck has standard factory LEDs, the entire housing or specific diode boards must be replaced rather than individual bulbs. The chart below covers the traditional replaceable bulb specs found on halogen-equipped or standard-spec trims.

LED vs halogen upgrade considerations

Upgrading a commercial truck from halogen to LED requires careful consideration due to the T680’s advanced multiplexed wiring system (controlled by the Cab Electronic Control Unit, or CECU).

• CANBUS Errors and Flickering: The CECU monitors voltage drops to detect burned-out bulbs. Because aftermarket LEDs draw significantly less power than halogens, the truck’s computer may throw a dash error or cause the lights to strobe. You will likely need CANBUS-ready LED bulbs or an inline load resistor/anti-flicker harness to trick the computer.
• Beam Pattern Compliance: Commercial trucks are strictly monitored by the DOT. Throwing a cheap LED bulb into a halogen reflector housing can scatter light and blind oncoming traffic. Always ensure your LED replacements mimic the exact filament location of the original H11 or H9 bulb to maintain a clean cutoff line.
• Space and Cooling: LED bulbs have bulky heat sinks or cooling fans. Check the clearance behind the T680’s headlight dust covers before buying to ensure the housing can still be sealed.

How to replace each bulb

• Low and High Beam Headlights: Tilt the hood forward. Access to the rear of the headlight housing is completely open on the T680, making this one of the easiest trucks to service. Simply remove the rubber dust cover, twist the H11 or H9 bulb counterclockwise, unplug the harness, and install the new bulb. Do not touch the new glass bulb with your bare hands.
• Fog Lights: These are accessed from under the bumper. You may need to remove a small splash shield depending on the aerodynamic package installed on your rig. Twist to remove.
• Front Turn Signals: Located in the main headlight assembly. Twist the bulb socket out from behind the housing and pull the 3157NA bulb straight out.
• Rear Brake/Turn/Tail Lights: Most 2024 Kenworths use standard 4-inch round DOT LED fixtures enclosed in a rubber grommet. If one fails, use a flathead screwdriver to carefully pry the fixture out of the rubber grommet, unplug the 3-prong pigtail, and push a new sealed fixture in.
• Side Markers / License Plate: The 194 bulbs can be pulled straight out of their sockets. For sealed aerodynamic roof markers, two Phillips screws usually hold the assembly in place, and you will replace the entire small unit.

Common lighting issues for this generation

• Integrated LED Failures: On the fully LED Next Gen T680 headlights, a failure in the signature swooping DRL or main beam often requires replacing the entire expensive assembly, which can be a pain point for owner-operators out of warranty.
• Moisture Intrusion: Heavy vibration and extreme weather can wear down the seals on the headlight dust covers. If you see condensation inside your halogen housings, remove the cover, let it dry out, and replace the rubber seal to prevent premature bulb failure.
• Chafed Wiring: Because the hood hinges open, the wiring harness routing down the hood pivot points can occasionally chafe over hundreds of thousands of miles, leading to intermittent headlight or turn signal drops. Always check the harness if a new bulb doesn’t fix your lighting issue.

Need help diagnosing a stubborn multiplex wiring issue or upgrading your rig's lighting to DOT-compliant LEDs? Find a trusted shop on Repairius.