2021 Peterbilt 579 Fuse Box Diagram & Amperage
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Quick answer
On the 2021 Peterbilt 579, you'll find the primary fuse box inside the cab, on the driver's side. It is located behind a removable kick panel, to the left of the clutch pedal. Some fuses and relays may also be found in a secondary panel located in the sleeper cab, if your truck is so equipped.
Driver's Side Kick Panel Fuse Box
This is the main fuse box for your Peterbilt 579. Always confirm the fuse layout with the diagram printed inside your fuse box cover, as configurations can vary based on your truck's specific options and trim level.
| Fuse # | Amp | Color | Circuit / Component Protected |
|---|---|---|---|
| F1 | 15A | Blue | ABS ECU |
| F2 | 10A | Red | Ignition Switch |
| F3 | 20A | Yellow | Cigar Lighter 1 |
| F4 | 20A | Yellow | Cigar Lighter 2 |
| F5 | 10A | Red | Radio, Infotainment System |
| F6 | 15A | Blue | Blower Motor |
| F7 | 10A | Red | Headlight, Low Beam (Left) |
| F8 | 10A | Red | Headlight, Low Beam (Right) |
| F9 | 15A | Blue | Headlight, High Beam (Left) |
| F10 | 15A | Blue | Headlight, High Beam (Right) |
| F11 | 10A | Red | Tail/Park Lights |
| F12 | 15A | Blue | Brake Lights |
| F13 | 30A | Green | ECM/PCM |
| F14 | 20A | Yellow | Fuel Pump |
| F15 | 10A | Red | Starter Relay |
| F16 | 20A | Yellow | Trailer Brake Controller |
| F17 | 10A | Red | A/C Clutch |
| F18 | 15A | Blue | Airbag Module |
| R1 | - | - | Ignition Relay |
| R2 | - | - | Starter Relay |
| R3 | - | - | Fuel Pump Relay |
| R4 | - | - | Headlight Relay |
| R5 | - | - | A/C Clutch Relay |
Sleeper Cab Fuse Box (If Equipped)
For trucks with a sleeper cab, a secondary fuse panel is often located here to power accessories and systems specific to the sleeper area.
| Fuse # | Amp | Color | Circuit / Component Protected |
|---|---|---|---|
| S1 | 20A | Yellow | Sleeper 12V Power Outlet |
| S2 | 15A | Blue | Sleeper Dome Lights |
| S3 | 10A | Red | Sleeper HVAC Blower |
| S4 | 15A | Blue | Refrigerator Power |
How to test a fuse
To test a fuse, first turn off the ignition and the component that is not working. Locate the fuse box and remove the fuse in question. You can often tell if a fuse is blown by a visual inspection — look for a broken filament inside the plastic casing. For a more accurate test, use a multimeter set to the continuity setting. Place a probe on each of the fuse's metal tabs. If the multimeter beeps or shows a reading of zero, the fuse is good. If it remains silent or shows an open circuit, the fuse is blown and needs to be replaced with a new fuse of the same amperage rating.
Common blown fuses on this vehicle
- Cigar Lighter/12V Power Outlet: These fuses often blow due to faulty phone chargers or other devices plugged into them. Before replacing the fuse, unplug all devices from the outlets and inspect them for damage.
- Trailer Lights/Brake Controller: Issues with trailer wiring are a common cause for these fuses to blow. Inspect the trailer wiring harness and the trailer itself for any shorts or corrosion.
- Headlights: If a headlight fuse blows, it could be due to a faulty bulb or a problem with the headlight wiring. Replace the bulb first, as this is the most common and easiest fix.
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Before you pull a fuse on the 2021 Peterbilt 579
- Use the label printed on the panel cover or the owner's manual for your exact build. Layouts change with options, model year and build date, so a chart for another truck can be wrong.
- Replace a blown fuse only with the same amp rating. A larger fuse can let wiring overheat.
- A fuse that blows again right away means a short or failing component downstream. Find the cause before replacing it again.
- A good fuse doesn't prove the circuit works — relays, grounds and connectors fail too.
- Many heavy trucks have more than one power distribution point (cab, under-hood or near the batteries), and some circuits use circuit breakers instead of fuses. Some systems have 24-volt starting circuits; confirm the voltage before testing.
- Disconnect the battery before working near high-current fuses or cables.
Learn more: How fuses, relays and truck electrical systems work · Find mobile truck repair
More specs for the 2021 Peterbilt 579
Oil Capacity & Filter
Capacity, weight, filter PN, drain plug torque, change interval.
Fluid Type Specs
Engine oil, coolant, ATF, diff, brake, PS, DEF — with OEM spec numbers.
Coolant Capacity & Type
Total system capacity, OEM coolant spec, flush interval, bleed tips.
Transmission Fluid & Service
Trans model, fluid spec, capacity, filter PN, service interval.
Torque Specifications
Lug nuts, drain plug, caliper, axle nut, plug, key fasteners.
Brake Pad & Rotor Specs
Pad PNs, rotor size, min thickness, caliper torque.
Tire Size & Pressure
OEM size, cold psi, bolt pattern, wheel size, TPMS.
Battery Size & Group
Group size, CCA, AGM/flooded, dimensions, reset note.
A/C Refrigerant & Oil
R-134a or R-1234yf, charge oz, PAG oil spec.
Bulb Sizes (Headlight, Tail, Fog)
Headlight, fog, tail, turn, reverse, interior.
Factory Maintenance Schedule
Service intervals by mileage, severe-duty notes, known issues.
Towing Capacity & Payload
Max tow, payload, GVWR/GCWR, hitch class by trim.
Serpentine Belt Routing & Length
Belt routing, length, rib count, OEM + aftermarket PNs.
Wheel Alignment Specifications
Camber, caster, toe ranges (front & rear), adjustability notes.
Paint Color Codes
All factory colors with paint codes, sticker location, touch-up tips.
Wiper Blade Sizes
Driver/passenger/rear blade size, attachment, OEM + cross-refs.
Spark Plug Type & Gap
Plug PN, gap, torque, interval by engine.
Transmission & Axle Gear Ratios
Trans gear ratios, axle ratios, RPO codes, tow vs MPG impact.
Key Fob Programming
DIY programming steps, FCC ID, fob PN, battery, transponder.
Same spec — other model years
Maintenance & repair guides
2021 Peterbilt 579 Maintenance Schedule →
Available maintenance guidance; confirm the manufacturer schedule.
Repair planning references →
Plan the scope of work; detailed procedures need configuration-matched evidence.
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