2019 Peterbilt 389 Fuse Box Diagram & Amperages

As an ASE-certified master technician, I know firsthand that tracking down electrical gremlins on a heavy-duty rig can be a daunting task. The 2019 Peterbilt 389 is a classic long-nose highway legend, packed with modern multiplexed wiring and electronic control modules. Knowing exactly where your fuses and relays are located—and what circuits they protect—is essential for keeping your truck on the road and minimizing costly downtime.

Whether you have lost power to your sleeper cab 12V outlets, your trailer lights are out, or you are troubleshooting a no-start ECM issue, this reference guide will help you navigate the power distribution on your 389.

Note: Heavy-duty truck configurations vary wildly based on engine choice (Cummins ISX / X15 vs. PACCAR MX-13), sleeper size, and custom upfitting. The tables below represent the most common factory configuration. Always verify against the printed legend on your specific fuse box lid or owner’s manual.

Quick answer

On a 2019 Peterbilt 389, the fuses and relays are primarily split between two or three main locations depending on your sleeper configuration:

1. Main Dash Fuse Box (Cab Electrical Center): Located inside the cab on the driver’s side, usually behind a removable panel near the clutch pedal / lower left kick panel.
2. Under-Hood Power Distribution Center (PDC) / Firewall: Located under the hood, typically mounted on the firewall on the driver’s side. This handles high-amperage maxi fuses and relays for the engine, starter, and main cab power.
3. Sleeper Auxiliary Panel (If equipped): Located inside the sleeper, often under the bunk or behind a side access panel, controlling sleeper-specific HVAC, lighting, and power outlets.

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Main Dash Fuse Box (Cab Electrical Center)

The main interior fuse box handles most of the cab’s lighting, ignition, radio, and interior accessory circuits. It utilizes standard blade-style mini/ATO fuses.

Fuse #	Amp	Color	Circuit / Component Protected
F1	10A	Red	Ignition Switch / Key ON Power
F2	15A	Blue	Headlights - Low Beam (Multiplex control)
F3	15A	Blue	Headlights - High Beam
F4	20A	Yellow	Brake Lights / Stop Lamp Switch
F5	10A	Red	Turn Signals / Hazard Lamps
F6	15A	Blue	Tail / Park / Clearance Lights
F7	30A	Green	Blower Motor (Cab HVAC)
F8	15A	Blue	A/C Compressor Clutch Relay
F9	10A	Red	Airbag / Supplemental Restraint System
F10	20A	Yellow	Radio / Infotainment / Navigation
F11	20A	Yellow	Cigar Lighter / 12V Power Outlet 1
F12	20A	Yellow	12V Power Outlet 2 / CB Radio Feed
F13	10A	Red	Instrument Cluster / Gauges
F14	15A	Blue	Wiper Motor / Washer Pump
F15	10A	Red	Diagnostic Connector (OBD / 9-Pin J1939)
F16	30A	Green	Power Windows
F17	15A	Blue	Power Mirrors / Heated Mirrors
F18	20A	Yellow	Cabin Dome Lights / Map Lights

Common Relays in this panel:

• R1: Ignition Relay
• R2: Accessory Power Relay
• R3: Wiper Motor High/Low Relay
• R4: Blower Motor Relay

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Under-Hood / Firewall Power Distribution Center (PDC)

This high-amperage box provides main power feeds to the cab, protects the engine control modules, and safeguards trailer lighting circuits. It features larger Maxi fuses and heavy-duty relays.

Fuse #	Amp	Color	Circuit / Component Protected
M1	50A	Red	Main Cab Power Feed 1
M2	50A	Red	Main Cab Power Feed 2
M3	30A	Green	Engine Control Module (ECM / PCM) - Battery Power
M4	30A	Green	Fuel Pump / Lift Pump
M5	20A	Yellow	NOx Sensor / Aftertreatment Power
M6	40A	Orange	ABS System (Tractor)
M7	30A	Green	Trailer ABS Power Feed
M8	30A	Green	Trailer Brake Controller Power
M9	30A	Green	Trailer Tail / Marker Lights
M10	30A	Green	Trailer Turn / Stop Lights
M11	20A	Yellow	Transmission Control Module (TCM - if Auto)

Common Relays in this panel:

• Starter Relay: Controls the high-current pull-in coil for the starter motor.
• ECM Power Relay: Energizes the main engine harness when the key is turned on.
• Fuel Heater Relay: (If equipped) Controls the diesel fuel heater for cold weather operation.

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Sleeper Auxiliary Fuse Box (If Equipped)

If your 389 is outfitted with a sleeper, there will typically be a secondary box to prevent sleeper accessories from overloading the cab circuits.

Fuse #	Amp	Color	Circuit / Component Protected
S1	30A	Green	Sleeper HVAC Blower Motor
S2	15A	Blue	Sleeper Interior Lighting
S3	20A	Yellow	Refrigerator / Cooler Power
S4	20A	Yellow	Sleeper 12V Outlets / USB
S5	30A	Green	Inverter Power / Auxiliary Feed

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How to test a fuse

When a component fails, checking the fuse should always be your first step. Here is the ASE-certified method for testing fuses quickly and accurately:

1. The Visual Inspection: Pull the suspect fuse using fuse pullers or needle-nose pliers. Hold it up to a light source. If the metal filament inside the plastic casing is broken or blackened, the fuse is blown and needs replacement.
2. The Test Light Method (Recommended): You don't even need to remove the fuse for this. Attach a 12V test light clamp to a good metal ground. Turn the ignition key to the "ON" position. Touch the tip of the test light to the small metal testing tabs exposed on the top of the fuse. If the test light illuminates on one side but not the other, the fuse is blown. If it lights up on both sides, the fuse is good, and your problem lies deeper in the circuit.
3. The Multimeter Method: Set your digital multimeter to the continuity setting (the one that beeps). Touch one probe to each test tab on top of the fuse. A continuous beep means the fuse is intact. No beep indicates an open (blown) fuse.

Common blown fuses on this vehicle

Heavy-duty trucks face a lot of vibration and accessory demand. On the Peterbilt 389, here are the most common fuses we replace in the shop:

• Trailer Lighting Fuses (M9, M10): Trailers are notorious for having rubbed wires, poor grounds, or corrosion in the 7-way plug. If your trailer lights go out but the tractor lights work, check the firewall PDC fuses and thoroughly inspect your 7-way pigtail before replacing the fuse.
• Cigar Lighter / 12V Outlets (F11, F12): Drivers plug in high-draw accessories like microwaves, coffee makers, and malfunctioning phone chargers into standard 12V outlets. If an outlet dies, check this fuse. (For heavy appliances, always wire directly to the battery via a proper inverter).
• CB Radio Feed: Often tapped into 12V accessory circuits. If a CB is improperly grounded or the power wire rubs against the metal dash frame, the fuse will pop to protect the wiring.

Important: Never replace a blown fuse with one of a higher amperage rating. Doing so removes the circuit's protection and can lead to melted wiring or even a cab fire.

If you keep blowing the same fuse, or if you're dealing with multiplex wiring issues that a simple fuse replacement won't fix, it’s time to call in a professional.

Find a trusted shop on Repairius.