2018 Kenworth W900 Fuse Box Diagram & Amperage

Quick Answer

The 2018 Kenworth W900 typically has multiple fuse box locations to manage the complex electrical systems. The primary fuse boxes are located:

• Under-hood: Usually on the passenger side firewall or near the battery box, housing fuses and relays for major engine and chassis components.
• Dash Kick-Panel (Cabin): Often located on the passenger side kick panel or behind a removable access panel in the dashboard, containing fuses for interior accessories and cabin electronics.

Always consult your specific truck's owner's manual and the labels on the fuse box covers for the most accurate information regarding fuse locations and ratings, as variations can exist based on trim level and installed options.

Under-hood Fuse Box

The under-hood fuse box on the Kenworth W900 typically contains higher amperage fuses and relays for critical systems such as the engine control module (ECM), fuel pump, ignition, starter, headlights, and ABS. The exact layout can vary, but a common configuration is as follows:

Relay Locations (Under-hood):

• R1: Starter Relay
• R2: Fuel Pump Relay
• R3: HVAC Blower Relay
• R4: Headlight Relay (Low Beam)
• R5: Headlight Relay (High Beam)
• R6: Main Ignition Relay
• R7: A/C Clutch Relay
• R8: Cooling Fan Relay

Dash Kick-Panel Fuse Box (Cabin)

This fuse box manages the electrical components within the cabin, including the radio, instrument cluster, interior lights, power windows, and various accessory outlets. Its exact location can vary, but it's commonly found behind a panel on the passenger side kick panel or dashboard.

Relay Locations (Cabin):

• R1: Accessory Relay (Switched)
• R2: Power Window Relay
• R3: Wiper Motor Relay
• R4: HVAC Fan Relay (Low Speed)

How to Test a Fuse

Testing a fuse is a straightforward process that can help you diagnose electrical issues quickly. Here's how you can do it:

1. Safety First: Always turn off the ignition and any affected circuits before handling fuses.
2. Locate the Fuse Box: Refer to your owner's manual or the quick answer section above to find the correct fuse box.
3. Identify the Suspect Fuse: Look at the fuse box diagram (either on the lid or in your manual) to find the fuse for the circuit you're troubleshooting.
4. Visual Inspection: Pull the fuse out. Most modern fuses have a clear plastic body. Look at the small wire or filament inside. If it's broken or melted, the fuse is blown and needs to be replaced.
5. Use a Fuse Tester or Multimeter: For a more reliable test, especially if the fuse isn't clear, use a fuse tester or multimeter:
   • Fuse Tester: Insert the fuse into the tester. If the light illuminates, the fuse is good. If not, it's blown.
   • Multimeter: Set your multimeter to continuity mode (looks like a speaker icon). Touch the probes to the metal contact points on top of the fuse. A good fuse will show a reading close to zero ohms or beep, indicating continuity. A blown fuse will show an "OL" (open circuit) or no beep.
6. Replace with Correct Amperage: If you find a blown fuse, replace it with a new fuse of the exact same amperage (A) rating. Using a fuse with a higher amperage can lead to serious electrical damage or fire.

Common Blown Fuses on This Vehicle

On a heavy-duty truck like the Kenworth W900, certain fuses are more prone to blowing due to the demands on their circuits or common accessory usage. When troubleshooting, consider these common culprits:

• Cigar Lighter / 12V Power Outlets: These fuses often blow due to overloaded accessories (inverters, chargers) or faulty devices plugged into them. If your charging ports aren't working, check this first.
• Blower Motor: The blower motor for the HVAC system draws significant current, especially on higher settings. A fuse for this circuit might blow if the motor is overworking (e.g., due to a clogged cabin filter) or if there's an internal short.
• Trailer Brake Control: With the constant connection and disconnection of various trailers, the trailer brake circuit can experience shorts or overloads, leading to a blown fuse. If your trailer brakes aren't functioning, inspect this fuse and the wiring to the trailer connector.
• Headlights: While less common with modern LED systems, traditional halogen headlight circuits can blow fuses, especially if there's a short in the wiring or a faulty bulb.
• Auxiliary Power Outlets (Sleeper/Cabin): Similar to the dash outlets, any auxiliary power outlets used for refrigerators, microwaves, or other high-drain accessories can cause their respective fuses to blow.

What to Check First: If an electrical component stops working, always check its specific fuse first. If the fuse is good, then you can broaden your diagnosis to relays, wiring, and the component itself.

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