2020 Peterbilt 389 Fuse Box Diagram & Amperage
Comprehensive guide to fuse locations and circuits in your Peterbilt 389
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This guide provides a comprehensive overview of the fuse box locations, diagrams, and amperage ratings for the 2020 Peterbilt 389. Identifying the correct fuse and its rating is crucial for diagnosing electrical issues and ensuring the proper functioning of your truck's systems.
Quick Answer
The 2020 Peterbilt 389 typically has three primary fuse box locations:
- Under-hood: Located on the driver's side, often near the firewall or battery box.
- Dash Kick-Panel: Located behind a removable panel on the passenger and/or driver's side kick panel.
- Rear Cab/Sleeper: Usually situated in the rear of the cab or within the sleeper compartment on models equipped with one.
Always verify the exact fuse box location and legend printed on the fuse box lid, as configurations can vary slightly due to trim levels or custom installations.
Under-hood Fuse Box
The under-hood fuse box typically houses fuses for critical engine functions, high-current circuits, and trailer connections. Relays for components like the starter, engine control, and fan clutch are also often found here.
Common Fuses & Circuits:
| Fuse # | Amp | Color | Circuit / Component Protected |
|---|---|---|---|
| F1 | 20A | Yellow | ECM/PCM (Engine Control Module/Powertrain Control Module) |
| F2 | 15A | Blue | Fuel Pump |
| F3 | 20A | Yellow | Ignition Switch (Main) |
| F4 | 30A | Green | Starter Relay |
| F5 | 10A | Red | Headlights (Low Beam - Left) |
| F6 | 10A | Red | Headlights (Low Beam - Right) |
| F7 | 15A | Blue | Headlights (High Beam - Left) |
| F8 | 15A | Blue | Headlights (High Beam - Right) |
| F9 | 10A | Red | Tail Lights / Marker Lights |
| F10 | 20A | Yellow | ABS (Anti-lock Braking System) Controller |
| F11 | 30A | Green | Trailer Brake Controller |
| F12 | 20A | Yellow | Trailer Auxiliary Power |
| F13 | 10A | Red | Horn |
| F14 | 15A | Blue | Windshield Wipers |
Relay Locations: Though specific positions vary, common relays found here include the Starter Relay, ECM Power Relay, Fuel Pump Relay, and ABS Relay.
Dash Kick-Panel Fuse Box (Driver's Side)
This fuse box often contains fuses for in-cab accessories, lighting, and convenience features.
Common Fuses & Circuits:
| Fuse # | Amp | Color | Circuit / Component Protected |
|---|---|---|---|
| F1 | 15A | Blue | Radio/Infotainment System |
| F2 | 10A | Red | Instrument Cluster |
| F3 | 20A | Yellow | Blower Motor (HVAC) |
| F4 | 10A | Red | A/C Clutch |
| F5 | 15A | Blue | Cigarette Lighter / 12V Outlet (Dash) |
| F6 | 10A | Red | Cabin Fuse (Interior Lights) |
| F7 | 5A | Tan | Airbag System |
| F8 | 10A | Red | Brake Lights |
| F9 | 10A | Red | Turn Signals/Hazard Lights |
| F10 | 15A | Blue | Power Windows (Driver) |
| F11 | 10A | Red | Mirror Adjustments |
| F12 | 20A | Yellow | Auxiliary Power Outlet (Console) |
Relay Locations: Relays for accessories like the blower motor, power windows, and auxiliary power outlets might be located near this fuse box.
Rear Cab/Sleeper Fuse Box
For models equipped with a sleeper, this fuse box provides power to sleeper area amenities, additional lighting, and sometimes auxiliary heating/cooling units. The exact location can vary, but it
Before you pull a fuse on the 2020 Peterbilt 389
- 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 2020 Peterbilt 389
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
2020 Peterbilt 389 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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