2020 Peterbilt 579 Fuse Box Diagram & Amperage

Quick answer

The 2020 Peterbilt 579 has two main fuse and relay centers:

• Cab Fuse Box: Located in the driver-side kick panel, near the clutch pedal or dead pedal area.
• Engine Compartment Fuse Box: Found under the hood, typically on the driver's side near the firewall.

Note: Depending on the truck's specific configuration and options (like sleeper cabs or auxiliary power units), there may be additional inline fuses or smaller, dedicated fuse blocks for specific systems. Always check the legend printed inside your fuse box covers to verify the correct fuse positions and ratings for your exact vehicle, as variations are common.

Cab Fuse Box (Driver-Side Kick Panel)

This fuse panel services the majority of the cab's interior and body electrical components. You will need to remove the kick panel cover to access it.

Engine Compartment Fuse Box

This box contains high-amperage fuses and relays that protect the engine, chassis, and critical powertrain components. It is located under the hood, usually on the driver's side.

How to test a fuse

A fuse is a simple protection device. If a circuit draws too much current, a thin wire inside the fuse melts and breaks the circuit to prevent damage. Visually inspecting a fuse is the quickest test.

1. Turn off the ignition and the component that isn't working.
2. Locate and remove the fuse. Use a fuse puller (often found in the fuse box) or a pair of needle-nose pliers.
3. Inspect the wire. Hold the fuse up to the light. If it's a good fuse, you will see an intact, S-shaped wire inside the plastic body. If it's a blown fuse, the wire will be broken or have a visible gap.
4. Use a multimeter (optional). For a more definitive test, set your multimeter to the continuity setting (it often has a sound symbol). Touch the probes to each of the two metal prongs on top of the fuse. If the multimeter beeps, the fuse is good. If it remains silent, the fuse is blown and has no continuity.
5. Replace if necessary. If the fuse is blown, replace it with a new fuse of the exact same amperage rating. Using a higher-rated fuse can cause a fire.

Common blown fuses on this vehicle

• Cigar Lighter / 12V Power Outlets (Fuse F7, F8): This is one of the most common blown fuses, usually caused by a faulty phone charger, a coin falling into the socket, or plugging in a device that draws too much power. Before replacing the fuse, inspect the socket for any foreign objects.

• Blower Motor (Fuse F16): If your HVAC fan suddenly stops working on all speeds, this fuse is the first thing to check. If the new fuse blows immediately or soon after, it often indicates a failing blower motor or a bad blower motor resistor that is drawing excessive current.

• Trailer Brake / Marker Lights (Fuses F113, F114): Problems with trailer wiring are a frequent cause for these fuses blowing. A short circuit in the trailer's wiring harness or a faulty light on the trailer itself will cause the fuse in the truck to blow to protect the system. Check the trailer-side wiring and connectors first before suspecting an issue with the truck.

• Radio / Infotainment (Fuse F12): If your radio or center screen is dead, check this fuse. While it can blow on its own, it sometimes indicates an internal fault in the head unit or a short in the wiring behind the dash.

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