2015 Kenworth T680 Bulb Size Guide: Headlight, Tail, Fog & More

As an ASE-certified master technician who has spent countless hours diagnosing and repairing heavy-duty truck electrical systems, I know that keeping your 2015 Kenworth T680 properly illuminated is critical for safety and compliance. The Kenworth T680 is a highway workhorse, and its lighting system represents a transition period where fleets were moving from traditional halogen bulbs to more efficient factory LEDs and HIDs.

Whether you are performing routine maintenance before a long haul or upgrading your fleet's visibility, knowing the exact bulb sizes for your T680 is essential. Below is the comprehensive guide to the lighting on a 2015 Kenworth T680.

Quick Reference

Note: The 2015 Kenworth T680 often came with different trim levels and fleet specifications. Many rear lighting components on heavy-duty trucks are sealed LED units (often standard 4-inch round pigtail fixtures) rather than replaceable bulbs. Always check your specific housing before ordering replacements.

LED vs Halogen Upgrade Considerations

Upgrading the forward lighting on a Class 8 truck like the T680 is one of the most common modifications drivers make. However, transitioning from halogen to aftermarket LED bulbs requires careful consideration:

• CANBUS Errors and Flickering: The T680 relies on a multiplexed wiring system. The chassis node monitors electrical draw to detect burnt-out bulbs. Because LEDs draw significantly less power than halogens, the system may throw a "Check Light" dash error or cause the headlights to flicker. You will likely need CANBUS decoders (load resistors) installed inline with your new LED bulbs to mimic the halogen power draw.
• Housing Limitations: Putting an LED bulb into a halogen projector housing can sometimes result in scattered light, blinding oncoming traffic. Ensure you purchase high-quality LED bulbs designed to replicate the halogen filament's exact focal point, especially for the H11 low beams.
• Clearance Issues: LED bulbs often have large cooling fans or heat sinks on the back. The T680 headlight housing is relatively spacious, but always verify that the dust cap can still seal properly to prevent moisture intrusion.

How to Replace Each Bulb

Here are some technician tips for tackling the most common bulb replacements on your 2015 T680:

• Low and High Beam Headlights (H11/H9): You can access these from behind the headlight assembly. Tilt the hood forward for easy access. Twist the dust cap off, disconnect the wiring harness, and twist the bulb counterclockwise to remove it. Avoid touching the glass of the new halogen bulbs with your bare hands, as the oil from your skin can cause premature failure.
• Fog Lights (H11): Located in the lower bumper, these are accessed from underneath or behind the bumper. You may need to remove a splash shield depending on the bumper style.
• Front Turn Signals (3157): These are housed within the main headlight assembly. Similar to the headlights, they are accessed from the rear. Twist the socket out and pull the bulb straight out.
• Rear Lighting (Brake, Tail, Turn, Reverse): Most T680s utilize sealed 4-inch round LED lights mounted in the rear light bar or mud flap hangers. If one fails, you don't replace a bulb; you replace the entire sealed unit. Simply pry the light out of the rubber grommet and unplug the 3-prong pigtail connector.
• Side Markers and License Plate (194): Standard T10 wedge bulbs. Side markers on the fairings can be twisted out from behind, while the license plate light usually requires a Phillips screwdriver to remove the lens cover.
• Interior Dome/Map Lights: Carefully pry the plastic lens covers off with a non-marring trim tool. The festoon (211-2) or wedge (194) bulbs pull straight out. Disconnect the batteries if you are replacing these with LEDs to avoid popping the interior lighting fuse.

Common Lighting Issues for this Generation

The 2015 Kenworth T680 is a robust machine, but the lighting system has a few known quirks. The most common issue I see in the shop is moisture intrusion in the front headlight assemblies, which can blow expensive HID bulbs or corrode halogen connectors. Make sure the rear dust caps are always secured tight and the O-rings are intact.

Another frequent problem involves the chassis node system shutting down a lighting circuit due to a perceived short. If you have a light out, and replacing the bulb doesn't fix it, the chassis node may need to be reset with a diagnostic tool or by doing a hard battery disconnect, provided the underlying wiring issue (often a chafed wire near the frame rails) has been repaired.

Maintaining the lighting on your rig isn't just about passing DOT inspections; it's about keeping you and everyone else on the road safe. If you run into electrical gremlins or need a major lighting overhaul, don't hesitate to seek professional help. Find a trusted shop on Repairius.