2025 Peterbilt 389 Fuse Box Diagram & Amperage Guide
Locate and identify the fuses and relays in your 2025 Peterbilt 389 dash and engine bay.
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A blown fuse can bring your commercial rig to a screeching halt or knock out critical interior comforts on a long haul. Knowing exactly where your fuses are and what they control is a must for any driver or fleet mechanic. Below is a comprehensive guide to the fuse box locations, amperage ratings, and circuit diagrams for the 2025 Peterbilt 389.
Quick answer: Where are the fuse boxes on a 2025 Peterbilt 389?
On the 2025 Peterbilt 389, the fuses and relays are split into two primary locations:
- The Main Dash Fuse Box (Cabin Power Distribution Center): Located inside the cab, typically behind the lower center dash panel or near the passenger-side glovebox area. This panel controls interior components like the radio, 12V outlets, HVAC blower, and lighting.
- The Under-Hood Power Distribution Center (Engine PDC): Mounted in the engine bay, usually attached to the driver's side firewall. This box handles heavy-draw and powertrain-critical systems like the ECM, starter, ABS, headlights, and trailer connections.
Note: Because Peterbilt 389s are highly customizable (Cummins vs. PACCAR engines, day cab vs. sleeper cab, various lighting packages), the exact fuse layout may vary slightly. Always verify with the printed legend on the inside of your specific fuse box lid.
Main Dash Fuse Box (Cabin PDC)
This fuse box manages the primary creature comforts, interior electronics, and dash controls. To access it, you may need to remove a trim panel on the lower center dash.
| Fuse # | Amp | Color | Circuit / Component Protected |
|---|---|---|---|
| F1 | 15A | Blue | 12V Cigar Lighter / Accessory Power Outlets |
| F2 | 10A | Red | Radio / Infotainment / CB Radio Power |
| F3 | 10A | Red | Ignition Switch / Key ON Power |
| F4 | 30A | Green | HVAC Blower Motor (Cabin) |
| F5 | 10A | Red | Instrument Cluster / Dash Backlighting |
| F6 | 15A | Blue | Cabin Lighting / Dome Lights |
| F7 | 10A | Red | Airbag / Supplemental Restraint System (SRS) |
| F8 | 20A | Yellow | Power Windows (Left/Right) |
| F9 | 15A | Blue | Power Door Locks |
| F10 | 10A | Red | Diagnostic Link Connector (OBD / 9-pin port) |
| F11 | 20A | Yellow | Sleeper Cab Accessory Feed (if equipped) |
| F12 | 15A | Blue | A/C Compressor Clutch |
Interior Relays: You will also find several relays in this panel, typically including the HVAC Blower Relay, Ignition Relay, and Accessory Relay.
Under-Hood Power Distribution Center (Engine PDC)
The under-hood PDC is located on the firewall on the driver's side. Unlatch the hood and locate the black rectangular box with a secure latching lid. This box protects the engine management, heavy lighting, and chassis braking systems.
| Fuse # | Amp | Color | Circuit / Component Protected |
|---|---|---|---|
| F20 | 30A | Green | Engine Control Module (ECM / PCM) - Unswitched |
| F21 | 20A | Yellow | Fuel Pump / Lift Pump |
| F22 | 15A | Blue | Headlights - Low Beam (Left/Right) |
| F23 | 15A | Blue | Headlights - High Beam |
| F24 | 20A | Yellow | Tail Lights / Parking Lights / Clearance Lights |
| F25 | 20A | Yellow | Brake Lights (Tractor) |
| F26 | 30A | Green | Anti-lock Braking System (ABS) - Bendix/WABCO |
| F27 | 30A | Green | Trailer Brake / Trailer ABS Power |
| F28 | 25A | Clear/White | Trailer Lighting Feed (Aux) |
| F29 | 10A | Red | Horn (Air Horn Solenoid / Electric) |
| F30 | 15A | Blue | Engine Fan Clutch |
Under-Hood Relays: Critical relays found in the engine PDC usually include the Starter Relay, ECM Power Relay, Fuel Pump Relay, and Headlight Relays.
How to test a fuse
When a system goes down on your Peterbilt 389, testing the fuse is the fastest way to begin diagnosing the problem.
- Visual Inspection: Pull the suspected fuse using a fuse puller or needle-nose pliers. Look at the U-shaped metal wire inside the colored plastic housing. If the metal strip is broken, burned, or melted, the fuse is blown and must be replaced.
- Multimeter Test: Set a digital multimeter to the "Continuity" setting (usually indicated by a sound wave symbol). Touch one probe to each metal leg of the fuse. If the multimeter beeps, the fuse has continuity and is good. If it is silent, the fuse is blown.
- Test Light (In-Circuit): With the fuse still installed and the key in the "ON" position, touch the tip of a grounded 12V test light to the small metal test points on the top of the fuse. If the test light illuminates on both sides, the fuse is good. If it only lights up on one side, the fuse is blown.
Pro-tip: Never replace a blown fuse with one of a higher amperage rating. Doing so can cause wires to overheat, melt, or start an electrical fire.
Common blown fuses on this vehicle
Heavy-duty trucks see a lot of vibration and harsh conditions, making electrical issues relatively common. If you drive a 2025 Peterbilt 389, keep an eye on these frequently blown circuits:
- 12V Cigar Lighter / Accessory Fuses: Drivers plug all sorts of inverters, phone chargers, and GPS units into the dash outlets. Cheap chargers can short out, immediately blowing the 15A accessory fuse. If this blows, check your charging cables and the socket for debris.
- Trailer Lighting / Trailer Brake Fuses: Hooking up to a different trailer every day means you are at the mercy of the trailer's wiring. A short in the trailer's tail lights or ABS system will quickly blow the 25A or 30A trailer feed fuses in your under-hood PDC. Always inspect the trailer pigtail connection and clean the pins.
- HVAC Blower Motor Fuse: Running the heat or A/C on high for thousands of hours puts a strain on the blower motor. If the motor begins to fail or the cabin air filter gets severely clogged, it will draw too much current and pop the 30A blower fuse or burn out the blower relay.
If you are dealing with a persistent short circuit or an electrical gremlin you just can't track down, don't risk damaging your rig's wiring harness.
Find a trusted shop on Repairius.
Before you pull a fuse on the 2025 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 2025 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
2025 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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