2017 Kenworth W900 Bulb Sizes (Headlight, Tail, Fog)

As an ASE-certified master technician with years of experience working on heavy-duty rigs, I know firsthand that lighting on a classic like the Kenworth W900 is about more than just aesthetics—it’s a critical safety issue. The 2017 Kenworth W900, with its iconic traditional styling, generally uses classic sealed-beam style headlight housings and standard commercial lighting footprints, though by 2017, many rolled off the assembly line (or out of the dealership) equipped with heavy-duty LED sealed units.

If you are looking to replace a burnt-out bulb, upgrade to modern LEDs, or troubleshoot a lighting issue, this guide covers everything you need to know about the 2017 Kenworth W900 bulb sizes.

Quick reference

Many 2017 W900s utilize sealed lighting modules rather than replaceable glass bulbs, especially for the exterior marker and tail lights. Below are the standard incandescent bulb sizes and their sealed-beam equivalents.

Note: Trim levels and custom factory orders heavily influence a W900's lighting. Standard fleets often ordered halogens and incandescent markers to save money, while owner-operators typically opted for full LED packages (like Truck-Lite or J.W. Speaker housings).

LED vs halogen upgrade considerations

Upgrading a 2017 Kenworth W900 from factory halogens or incandescent markers to LEDs provides massive improvements in nighttime visibility and electrical efficiency. However, there are a few heavy-duty considerations to keep in mind:

• Heated Lenses are a Must for Winter: Standard halogen sealed beams melt snow and ice naturally. LEDs do not generate forward heat. If you run northern routes, you must upgrade to heated LED headlights (like those from J.W. Speaker or Truck-Lite) to prevent ice buildup on your 4x6 lenses.
• Flicker and CANBUS: While the W900 is generally more traditional in its electrical architecture than the T680, installing LED turn signals without swapping to an LED-compatible heavy-duty flasher relay will result in hyper-flashing.
• Pigtail Adapters: Most 4x6 LED headlights are plug-and-play with the standard 3-prong (H4 style) wiring harness on the W900, making headlight upgrades relatively painless.

How to replace each bulb

• Headlights (Low and High Beam): The quad rectangular headlights are held in by a metal retaining ring. Remove the Torx or Phillips screws holding the stainless bezel, then remove the retaining ring screws (be careful not to touch the aiming screws). Pull the sealed beam out and disconnect the plug.
• Fog Lights: Depending on your bumper setup, these are usually accessible from underneath. For H3 bulbs, unclip the housing rear cover and release the spring clip. For sealed PAR36 lights, replace the entire unit via the retaining ring.
• Front Turn Signals (Fender/Pedestal): Many W900s use pedestal lights mounted on the fenders. To replace the bulb, remove the amber lens screws. If it’s a sealed LED unit, you will replace the entire housing and unclip the wiring harness routed under the fender.
• Rear Tail / Brake / Reverse / Markers: Commercial trucks heavily utilize standard 4-inch round or 2-inch/2.5-inch round sealed lights pushed into rubber grommets. You don't replace the bulb; you pry the sealed light out of the rubber grommet with a flathead screwdriver and unplug the 3-prong pigtail from the back.
• Dome/Map Lights: Carefully pry off the plastic interior lens covers using a plastic trim tool. The festoon (cylinder) bulbs easily pop out of their spring terminals.

Common lighting issues for this generation

The biggest enemy of any W900’s lighting system is the road environment. Magnesium chloride and road salt wreak havoc on the rear light pigtails. If a 4-inch round tail light fails, it is very often corroded contacts inside the 3-prong pigtail rather than a failed LED. Always pack your electrical connectors with dielectric grease.

Ground issues are also prevalent. If you notice all the lights on one side of your headache rack or bumper dimming, or if a turn signal causes the reverse lights to blink, you have a broken or corroded chassis ground. Trace the harness back to the frame rail and clean the grounding stud.

When dealing with heavy-duty commercial vehicle wiring, quality repairs are paramount to keeping the DOT off your back. If you are chasing a persistent electrical gremlin or want to do a full LED conversion on your rig, find a trusted shop on Repairius.