2025 Kenworth T680 Bulb Size Chart: Headlight, Tail Light, Fog Light & More

As an ASE-certified master technician who spends a lot of time working on heavy-duty commercial trucks, I know how critical proper lighting is for your safety and compliance. The 2025 Kenworth T680 is a technological marvel on the road, featuring heavily updated aerodynamics and modern electrical architectures. If you're managing a fleet or operating as an owner-operator, knowing exactly what replacement bulbs or assemblies you need will keep you out of the DOT weigh station penalty box.

Here is your comprehensive guide to the 2025 Kenworth T680 bulb sizes, covering headlights, tail lights, fog lights, and interior illumination.

Quick reference

Note: The 2025 Kenworth T680 Next Gen heavily utilizes integrated factory LED assemblies for its primary lighting to reduce maintenance and power draw. However, some base-level fleet specifications still use standard replaceable halogen bulbs. Always verify your truck's specific trim level.

LED vs halogen upgrade considerations

If your T680 came equipped with the base halogen projector headlamps, upgrading to aftermarket LEDs is a common modification. However, modern Kenworths use sophisticated multiplex electrical systems and CANBUS monitoring.

• CANBUS Errors: Installing a standard LED bulb in a halogen circuit will almost certainly trigger a "Bulb Out" warning on your digital dash due to the lower power draw. You will need high-quality LED bulbs with built-in CANBUS decoders or external load resistors to prevent flickering and dashboard errors.
• Integrated Assemblies: If your truck features the premium factory LED headlights, the individual "bulbs" inside the housing cannot be replaced. If a low beam or DRL strip fails, the entire headlight assembly must be replaced.
• Beam Pattern: When upgrading halogen projectors to LED, ensure the LED diode alignment matches the original halogen filament. Misaligned bulbs in heavy-duty trucks cause severe glare for oncoming traffic.

How to replace each bulb

• Headlights (Low/High/Turn): Tilt the hood forward for complete access to the rear of the headlight housings. For halogen setups, twist off the protective dust cap, unclip the wiring harness, and twist the H11 or H9 bulb counterclockwise to remove. Ensure the dust cap is sealed tightly upon reinstallation.
• Fog Lights: Accessed from underneath the front bumper. Most 2025 T680s use integrated LED fog assemblies held in by Torx or 10mm bolts.
• Rear Tail / Brake / Turn / Reverse: Standard Kenworth configurations use rubber grommet-mounted 4-inch round fixtures on the rear light bar. Simply pry the rubber grommet away from the metal bracket with a flathead screwdriver, unplug the 3-prong pigtail, and push in a new sealed unit.
• Side Markers & Cab Lights: The aerodynamic cab markers on the roof and sleeper are generally sealed LED strips. They require unscrewing the housing from the exterior and disconnecting the harness inside the roof cavity.
• Interior Dome/Map Lights: Carefully pry the clear plastic lens covers down using a non-marring plastic trim tool. The 211-2 festoon bulbs snap in and out of their metal tension prongs.

Common lighting issues for this generation

While the newest generation of the T680 is highly reliable, heavy-duty applications take a toll on lighting components.

• Moisture in Headlights: The massive aerodynamic headlight housings on the T680 are prone to minor condensation in high-humidity/rapid-temperature-change environments. If water begins to pool at the bottom of the lens, the housing seal has failed and requires replacement.
• Chafed Wiring Harnesses: Due to the vibrations of the chassis and hood movement, the wiring harness leading to the headlight assemblies can chafe over time. If a new bulb doesn't fix a light outage, inspect the harness at the hood hinge pivot points.
• Corroded Rear Pigtails: The rear light bar is exposed to road salt and grime. If your rear brake or turn signals fail, check the 3-prong pigtail connectors for green corrosion before replacing the sealed light unit. Dielectric grease is your best friend here.

Don't let a burnt-out bulb result in a costly DOT violation. If you are dealing with complex CANBUS electrical issues or need assistance with full assembly replacements, get it fixed by a professional. Find a trusted shop on Repairius.