2015 Kenworth W900 Bulb Sizes (Headlight, Tail, Fog)

As an ASE-certified master technician, I’ve worked on countless heavy-duty trucks, and the iconic Kenworth W900 is one of my absolute favorites in the bay. When it comes to maintaining a 2015 Kenworth W900, lighting is critical for safety, DOT compliance, and nighttime visibility over long hauls. Whether you are running the classic quad headlight setup or the dual large rectangular buckets, keeping your bulbs shining bright is a top priority.

Below is your comprehensive guide to the 2015 Kenworth W900 bulb sizes, including upgrades and common issues.

Quick reference

Because the W900 is a highly customizable Class 8 truck, your exact lighting setup may vary based on factory specs and aftermarket modifications. However, here are the most common OEM and standard replacement sizes for the 2015 generation:

Note: By 2015, many Kenworths rolled off the assembly line with sealed LED fixtures for clearance, marker, and tail lights. If your housing is a sealed LED unit, you must replace the entire housing rather than a standalone bulb inside it.

LED vs halogen upgrade considerations

Upgrading a 2015 Kenworth W900 from standard halogen sealed beams to full LED headlights is one of the most popular modifications for owner-operators.

Sealed Beam Upgrades: Rather than replacing a tiny bulb inside a housing, you will usually replace the entire 7x6 (200mm) or 4x6 (165mm) sealed beam assembly with a DOT-approved LED fixture. Look for units from reputable brands that offer a sharp cutoff line so you do not blind oncoming traffic.

CANBUS and Anti-Flicker: While heavy-duty trucks are generally less finicky than modern luxury cars regarding CANBUS systems, LED headlights draw significantly less power. This can sometimes cause a flickering issue or trigger a bulb-out warning. In these cases, you’ll need to wire in a standard H4 anti-flicker harness or load resistor.

Turn Signals: If you are swapping standard incandescent 1157 pedestal turn signals for LED replacement bulbs, you will likely encounter hyper-flashing. Upgrading your truck's flasher relay to an LED-compatible (electronic) flasher unit will solve this immediately and is much easier than wiring load resistors into the truck's harness.

How to replace each bulb

Here are a few quick tips from the shop floor on replacing the lights on your W900:

• Headlights (Low/High Beam): To replace the sealed beams, remove the screws holding the stainless steel or chrome bezel on the front of the headlight bucket. Carefully pull the retaining ring off, slide the light forward, and unplug the 3-prong (or 2-prong for high-beam-only) pigtail at the back.
• Front Turn Signals (Fender/Pedestal): Depending on the style, these usually feature a few Phillips screws on the lens. Remove the amber lens, push in slightly on the bulb, and twist counterclockwise to release it.
• Rear Tail/Brake/Turn & Reverse Lights: Most heavy-duty W900s utilize 4-inch round rubber grommet-mounted lights on the rear light bar. To replace these, gently pry the sealed light unit out of the rubber grommet with a flathead screwdriver or plastic pry tool, unplug the 3-prong pigtail, and push the new unit in.
• Cab Clearance / Marker Lights: Often held in by two screws on a chrome base. Ensure the gasket underneath is intact when replacing these to prevent water intrusion into the cab roof.

Common lighting issues for this generation

The 2015 W900 is a tough, reliable workhorse, but a few common electrical issues can crop up with high mileage:

1. Corroded Pigtails: The rear light bar takes a beating from road salt and debris. If a tail light or reverse light stops working, check the 3-prong pigtail connector for green corrosion before assuming the light itself is dead. Dielectric grease is your best friend here.
2. Grounding Issues: Many heavy-duty truck lighting problems stem from a bad ground. If your lights are dimming, flickering, or acting erratically when you hit the brakes, trace the ground wire from the light housing back to the frame and ensure the connection is clean and tight.
3. Leaking Cab Markers: The gaskets on the roof clearance lights can dry rot over time, allowing moisture in. This will short out the bulb and potentially cause water damage to the interior headliner. Always inspect these seals during replacement.

When in doubt about wiring issues or chasing down electrical gremlins on your rig, it’s always best to consult a professional. Find a trusted shop on Repairius.