2018 Kenworth W900 Bulb Sizes

Quick reference

The 2018 Kenworth W900, a classic in the trucking world, primarily came equipped with a mix of halogen and, in some cases, optional LED lighting from the factory. While the W900 is known for its timeless design, its lighting can vary depending on the specific trim and options chosen by the original owner. Understanding these differences is key when looking to replace or upgrade your bulbs.

For the headlights, most 2018 W900 models utilize traditional halogen bulbs. The low beams typically take an H11 bulb, providing a good balance of brightness and lifespan. High beams are commonly H7 bulbs, offering a focused and powerful beam for maximum visibility on dark roads. Fog lights often use H10 or H16 bulbs, designed to cut through adverse weather conditions. It's important to note that some W900s, especially higher trims or those with premium packages, might have featured factory-installed LED headlight options. In such cases, replacing individual bulbs is usually not an option, and the entire headlight assembly would need to be replaced if there's a component failure.

The Day-Running Lights (DRL) often share functionality with the front turn signals, using a an 1157-style bulb, or could be integrated LEDs on models equipped with them. Front turn signals commonly use 3157 or 4157NALL amber bulbs, which are dual-filament bulbs serving both parking light and turn signal functions. Rear turn signals, brake lights, and tail lights on many W900s are either 1157 (for dual filament, like brake/tail) or 1156 (for single filament, like turn signal or reverse) halogen bulbs. However, it's increasingly common to find these functions handled by LED clusters from the factory, especially on newer W900 models or those with updated lighting packages. Reverse lights generally use an 1156 halogen bulb if not an integrated LED unit. When dealing with LED rear lighting, replacement usually means replacing the entire light assembly, not just a bulb.

License plate lights are typically small 194 wedge-style halogen bulbs, providing illumination for your rear plate. Side marker lights along the truck and trailer tend to be 194 bulbs as well, though many fleet operators and owners opt for LED upgrades in these locations for improved visibility and longevity. Inside the cab, dome and map lights frequently use a 578 festoon bulb, often found in interior fixtures, though many are migrating to LED as well for a brighter, more efficient interior light. Some W900s might have multiple interior light configurations, so it's always a good idea to visually confirm the bulb type before purchasing replacements.

LED vs halogen upgrade considerations

Upgrading your 2018 Kenworth W900 from halogen to LED bulbs can offer significant benefits, including brighter light output, longer lifespan, and lower power consumption. However, there are several considerations to keep in mind.

CANBUS Errors: Modern vehicles, including the Kenworth W900, often use a CANBUS (Controller Area Network Bus) system to monitor electrical components. Halogen bulbs draw more power than LEDs. When you replace a halogen bulb with an LED, the lower power draw can be misinterpreted by the CANBUS system as a "bulb out" error, triggering dashboard warning lights or causing hyper-flashing for turn signals. To prevent this, you'll often need to install CANBUS-compatible LED bulbs or separate load resistors in parallel with the LED bulbs.

Adapters Needed: For headlights, while the base types (H11, H7) might be the same, the physical size of LED bulbs (especially those with cooling fans or heatsinks) can be larger than their halogen counterparts. This might require minor modifications to the headlight housing or the use of specific adapters to ensure a proper fit and seal. Some LED kits come with their own drivers or modules, which also need to be mounted securely.

Beam Pattern and Legality: Not all LED "replacement" bulbs are designed to replicate the precise beam pattern of their halogen predecessors in a reflector or projector housing. A poorly designed LED can scatter light, creating glare for oncoming drivers and reducing your effective visibility. It's crucial to choose high-quality LED bulbs specifically designed for automotive use and, where applicable, ensure they meet DOT (Department of Transportation) regulations for your specific application. Factory LED assemblies are designed as a complete unit and are usually the best performance-wise.

How to replace each bulb

Replacing bulbs on your Kenworth W900 is generally straightforward, but always ensure the vehicle is off and the lights are cool before starting. Disconnect the battery for major electrical work.

• Headlights (Low/High Beam) & Fog Lights: Access is usually from behind the headlight assembly, often requiring the removal of a dust cap. Twist the bulb counter-clockwise to remove, unplug the electrical connector, and reverse the process for installation. Be careful not to touch the glass of new halogen bulbs.
• DRL & Front/Rear Turn Signals: Access is typically from behind the light housing. Twist the socket counter-clockwise to remove it from the housing, then pull the bulb straight out. Push the new bulb in firmly.
• Brake/Tail/Reverse Lights: For most W900s, these are accessed by removing the lens cover or, in many cases, twisting the bulb socket out from the back of the housing. Some larger truck lights may have multiple fasteners holding the entire assembly.
• License Plate Lights: Usually involves removing a small screw or two from the lens cover, then pulling out the old wedge bulb and pushing in the new one.
• Side Marker Lights: Similar to license plate lights, often a small lens with a single wedge bulb underneath, released by a screw or careful prying.
• Dome/Map Lights: Carefully pry off the lens cover (often with a small flat-head screwdriver), then either pull out the wedge bulb or use a tool to gently release the festoon bulb from its clips.

Common lighting issues for this generation

Owners of 2018 Kenworth W900s may encounter a few common lighting issues, mostly related to the harsh conditions commercial trucks endure.

• Vibration-Related Failures: Constant vibrations from road travel can loosen bulb filaments or electrical connections, leading to premature bulb failure or intermittent operation, especially with older halogen bulbs. Inspecting sockets for corrosion and ensuring secure connections is vital.
• Corrosion in Sockets: Exposure of the W900 to weather and road spray can lead to corrosion in bulb sockets, causing poor electrical contact and dim or non-functional lights. Cleaning sockets with electrical contact cleaner and a small brush can often resolve these issues.
• Wiring Harness Issues: The extensive wiring harnesses in a truck like the W900 are susceptible to wear and tear, chafing, or damage from road debris. This can lead to intermittent lighting problems or complete outages. A proper diagnostic involves checking continuity and voltage at various points in the circuit.
• Trailer Wiring Integration: Many lighting issues on a W900 can be traced back to problems with the trailer wiring harness or the truck's connection to it. Always check both the truck and trailer side when diagnosing issues that affect both.
• Factory LED Failures: While durable, if a factory LED unit fails (e.g., a few diodes go out in an assembly), it typically requires replacing the entire light assembly, which can be more costly than replacing a simple bulb.

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