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<h2>Quick Answer</h2>
<p>The 2018 Peterbilt 579 typically has multiple fuse box locations to manage the vehicle's extensive electrical systems. You'll generally find fuse boxes in the following locations:</p>
<ul>
<li><strong>Under-hood (Power Distribution Center):</strong> Located on the driver's side, often near the firewall or fender. This box manages high-current circuits and relays.</li>
<li><strong>Interior (Cab Fuse Panel):</strong> Usually located on the passenger side kick panel or behind a removable cover in the dashboard. This panel handles many of the cabin accessories and control modules.</li>
<li><strong>Chassis (Auxiliary Fuse Panel):</strong> Depending on the specific trim and options, an additional fuse panel might be found on the chassis, often near the battery box or a frame rail, for body-builder connections or specific accessories.</li>
</ul>
<h2>Under-hood Fuse Box (Power Distribution Center)</h2>
<p>This fuse box, often referred to as the Power Distribution Center (PDC), is responsible for many of the primary power circuits and relays crucial for engine operation and major vehicle functions. Location: Driver's side, often near the firewall or fender.</p>
<table>
<thead>
<tr>
<th>Fuse #</th>
<th>Amp</th>
<th>Color</th>
<th>Circuit / Component Protected</th>
</tr>
</thead>
<tbody>
<tr>
<td>F1</td>
<td>40A</td>
<td>Green</td>
<td>ECM/PCM Main Power</td>
</tr>
<tr>
<td>F2</td>
<td>30A</td>
<td>Green</td>
<td>Ignition Switch Main</td>
</tr>
<tr>
<td>F3</td>
<td>20A</td>
<td>Yellow</td>
<td>Fuel Pump Relay</td>
</tr>
<tr>
<td>F4</td>
<td>20A</td>
<td>Yellow</td>
<td>Starter Solenoid</td>
</tr>
<tr>
<td>F5</td>
<td>25A</td>
<td>Clear</td>
<td>ABS Module Power</td>
</tr>
<tr>
<td>F6</td>
<td>30A</td>
<td>Green</td>
<td>Headlight (Left)</td>
</tr>
<tr>
<td>F7</td>
<td>30A</td>
<td>Green</td>
<td>Headlight (Right)</td>
</tr>
<tr>
<td>F8</td>
<td>20A</td>
<td>Yellow</td>
<td>Trailer Brake Controller Main</td>
</tr>
<tr>
<td>F9</td>
<td>15A</td>
<td>Blue</td>
<td>Diagnostic Port (OBD-II/J1939)</td>
</tr>
<tr>
<td>F10</td>
<td>10A</td>
<td>Red</td>
<td>Horn</td>
</tr>
</tbody>
</table>
<h4>Under-hood Relay Locations (Common)</h4>
<ul>
<li><strong>R1:</strong> ECM/PCM Relay</li>
<li><strong>R2:</b> Fuel Pump Relay</li>
<li><strong>R3:</strong> Starter Relay</li>
<li><strong>R4:</strong> Headlight Relay (Low Beam)</li>
<li><strong>R5:</strong> Headlight Relay (High Beam)</li>
<li><strong>R6:</strong> HVAC Blower Motor Relay</li>
</ul>
<h2>Interior Fuse Box (Cab Fuse Panel)</h2>
<p>This panel, typically located behind the passenger side kick panel or a removable cover in the dashboard, controls many of the interior and accessory functions. Please note that fuse numbering and assignments can vary slightly based on specific trim levels and installed options. Always refer to the legend printed on the inside of your fuse box lid for the most accurate information.</p>
<table>
<thead>
<tr>
<th>Fuse #</th>
<th>Amp</th>
<th>Color</th>
<th>Circuit / Component Protected</th>
</tr>
</thead>
<tbody>
<tr>
<td>F1</td>
<td>10A</td>
<td>Red</td>
<td>Radio/Infotainment System</td>
</tr>
<tr>
<td>F2</td>
<td>15A</td>
<td>Blue</td>
<td>Cigar Lighter / 12V Outlet (Dash)</td>
</tr>
<tr>
<td>F3</td>
<td>15A</td>
<td>Blue</td>
<td>HVAC Blower Motor Control</td>
</tr>
<tr>
<td>F4</td>
<td>10A</td>
<td>Red</td>
<td>Cabin Lights (Dome/Map)</td>
</tr>
<tr>
<td>F5</td>
<td>10A</td>
<td>Red</td>
<td>Accessory Power Outlet (Sleeper)</td>
</tr>
<tr>
<td>F6</td>
<td>10A</td>
<td>Red</td>
<td>Brake Lights / CHMSL</td>
</tr>
<tr>
<td>F7</td>
<td>5A</td>
<td>Tan</td>
<td>ABS Warning Light</td>
</tr>
<tr>
<td>F8</td>
<td>10A</td>
<td>Red</td>
<td>Airbag System (SRS)</td>
</tr>
<tr>
<td>F9</td>
<td>15A</td>
<td>Blue</td>
<td>Wiper Motor</td>
</tr>
<tr>
<td>F10</td>
<td>10A</td>
<td>Red</td>
<td>Turn Signals / Hazard Lights</td>
</tr>
<tr>
<td>F11</td>
<td>15A</td>
<td>Blue</td>
<td>Power Windows (Driver)</td>
</tr>
<tr>
<td>F12</td>
<td>15A</td>
<td>Blue</td>
<td>Power Windows (Passenger)</td>
</tr>
<tr>
<td>F13</td>
<td>7.5A</td>
<td>Brown</td>
<td>Trailer ABS Power</td>
</tr>
<tr>
<td>F14</td>
<td>20A</td>
<td>Yellow</td>
<td>A/C Clutch</td>
</tr>
<tr>
<td>F15</td>
<td>5A</td>
<td>Tan</td>
<td>Instrument Cluster</td>
</tr>
<tr>
<td>F16</td>
<td>10A</td>
<td>Red</td>
<td>Daytime Running Lights (DRL)</td>
</tr>
<tr>
<td>F17</td>
<td>10A</td>
<td>Red</td>
<td>Park/Tail Lights (Left)</td>
</tr>
<tr>
<td>F18</td>
<td>10A</td>
<td>Red</td>
<td>Park/Tail Lights (Right)</td>
</tr>
<tr>
<td>F19</td>
<td>20A</td>
<td>Yellow</td>
<td>Heated Mirrors</td>
</tr>
<tr>
<td>F20</td>
<td>15A</td>
<td>Blue</td>
<td>Auxiliary Power Outlet (Cabin)</td>
</tr>
</tbody>
</table>
<h4>Interior Relay Locations (Common)</h4>
<ul>
<li><strong>R1:</strong> Accessory Delay Relay</li>
<li><strong>R2:</strong> Blower Motor Low Speed Relay</li>
<li><strong>R3:</strong> Wiper Motor Relay</li>
<li><strong>R4:</strong> Power Window Relay</li>
</ul>
<h2>Chassis Auxiliary Fuse Panel (Optional)</h2>
<p>Some Peterbilt 579 models, especially those with custom bodywork or extensive auxiliary equipment, may have an additional fuse panel located on the chassis. This is often found near the battery box, along the frame rail, or in a weatherproof compartment. Its contents are highly dependent on the vehicle's specific configuration and can include circuits for items such as:</p>
<ul>
<li>Liftgate Power</li>
<li>Trailer Auxiliary Power</li>
<li>Additional Work Lights</li>
<li>Specialized Equipment</li>
<li>Aftermarket Accessories</li>
</ul>
<p>Always consult your vehicle's specific owner's manual and any supplemental documentation for factory-installed or aftermarket auxiliary fuse panels.</p>
<h2>How to Test a Fuse</h2>
<p>Testing a fuse is a straightforward process that requires a basic understanding of electrical circuits and a few simple tools:</p>
<ol>
<li><strong>Turn Off the Vehicle:</strong> Always ensure the ignition is off and disconnect the battery if you're working near the main power distribution center to prevent accidental shorts or injury.</li>
<li><strong>Locate the Fuse:</strong> Identify the suspected blown fuse using your fuse box diagram.</li>
<li><strong>Visual Inspection:</strong> Many modern fuses have a visible wire element inside. If this wire is broken or charred, the fuse is blown.</li>
<li><strong>Use a Fuse Tester or Multimeter:</strong>
<ul>
<li><strong>Fuse Tester:</strong> A simple fuse tester lights up when a good fuse is inserted or touched across its test points.</li>
<li><strong>Multimeter:</strong> Set your multimeter to the continuity or ohm setting. Remove the fuse from its slot. Touch the probes to the metal contacts on each end of the fuse. A good fuse will show continuity (a very low resistance reading or a beep), while a blown fuse will show no continuity (an open circuit or "OL" reading).</li>
</ul>
</li>
<li><strong>Replace if Blown:</strong> Always replace a blown fuse with a new fuse of the exact same amperage rating and type. Using a fuse with a higher rating can lead to serious electrical damage or fire.</li>
</ol>
<h2>Common Blown Fuses on This Vehicle</h2>
<p>While any fuse can blow, some are more prone to failure due to their circuit's demands or common component issues. On a 2018 Peterbilt 579, common culprits can include:</p>
<ul>
<li><strong>Cigar Lighter / 12V Outlets:</strong> Frequently overloaded by phone chargers, portable refrigerators, or other accessories.</li>
<li><strong>Blower Motor:</strong> Can blow if the blower motor starts to fail or if there's an obstruction in the HVAC system causing it to draw excessive current.</li>
<li><strong>Headlights/Tail Lights:</strong> Bulbs failing or issues with wiring can sometimes cause these fuses to blow.</li>
<li><strong>Trailer Brake/Trailer Lights:</strong> Problems with trailer wiring, shorts in the trailer itself, or overloading can frequently blow these fuses. Always inspect trailer connections if you experience issues.</li>
<li><strong>Ignition/ECM Fuses:</strong> While less common for routine failure, if these blow, it typically points to a more significant electrical issue with a primary component or wiring short.</li>
</ul>
<p>If you experience a repeated fuse blow, it's crucial to investigate the underlying cause, as simply replacing the fuse without addressing the root problem can lead to more serious damage.</p>
<h2>Find a trusted shop on Repairius.</h2>
Before you pull a fuse on the 2018 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.
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