2018 Chevrolet Silverado 3500HD Fuse Box Diagram & Amperages

As an ASE-certified master technician, I frequently work on heavy-duty trucks like the 2018 Chevrolet Silverado 3500HD. Electrical issues are common, especially when towing heavy loads, adding aftermarket accessories, or dealing with trailer wiring. Finding the right fuse quickly can save you hours of diagnostic time and get you back on the road or the job site.

This guide provides the fuse box locations, diagrams, and amp ratings for the 2018 Chevrolet Silverado 3500HD, focusing on the most critical circuits like the ECM, fuel pump, trailer brakes, and 12V outlets.

Note: Fuse configurations can vary slightly based on cab size, engine type (Duramax Diesel vs. Gas), and trim level (WT to High Country). Always verify with the printed legend on the inside of your fuse box cover before replacing a fuse.

Quick answer

The 2018 Chevrolet Silverado 3500HD has three main fuse block locations:

1. Engine Compartment Fuse Block: Located under the hood on the driver’s side, near the battery.
2. Left Instrument Panel Fuse Block: Located on the driver’s side of the dashboard, behind a removable cover visible when you open the driver's door.
3. Right Instrument Panel Fuse Block: Located on the passenger’s side of the dashboard, behind a removable cover visible when you open the passenger's door.

Engine Compartment Fuse Block

The under-hood fuse block handles the heavy-duty power distribution for the powertrain, exterior lighting, ABS, and towing functions.

Key Relays in this box:

• Relay 69: Starter Relay
• Relay 70: Fuel Pump Relay
• Relay 72: A/C Control Relay
• Relay 75: Engine Control Relay

Left Instrument Panel Fuse Block

This fuse block primarily handles driver-side interior functions, infotainment, and the 12V power outlets (cigar lighters).

Right Instrument Panel Fuse Block

This fuse box manages passenger-side accessories, supplementary Body Control Module (BCM) circuits, and some climate control functions.

How to test a fuse

When an electrical component fails on your Silverado 3500HD, the fuse is the first thing you should check. Here is the proper way to test them:

1. Locate the right fuse: Use the legend on the inside of the fuse block cover (or the tables above) to find the specific fuse for your dead circuit.
2. Visual Inspection: Pull the fuse straight out using a fuse puller or needle-nose pliers. Look at the U-shaped metal element inside the colored plastic housing. If the metal band is broken or there is a black, scorch mark inside, the fuse is blown.
3. Use a Multimeter or Test Light: Sometimes a fuse looks perfectly fine but has a hairline fracture.
   • Turn the ignition to the "ON" position (do not start the engine).
   • Take a 12V test light and ground the clip to bare metal.
   • Touch the probe to the two small metal test points exposed on the top of the fuse while it is still plugged in.
   • If the test light illuminates on both sides, the fuse is good. If it lights up on only one side, the fuse is blown and must be replaced.
4. Replace with the exact amperage: Never replace a blown fuse with one of a higher amp rating (e.g., putting a 30A fuse in a 15A slot). This can cause wiring to overheat and potentially start a fire.

Common blown fuses on this vehicle

Heavy-duty trucks are worked hard, and some circuits are more prone to blowing fuses than others. If you own a 2018 Silverado 3500HD, keep a close eye on these:

• Trailer Stop/Turn and Trailer Brake Fuses (Under-hood #14, #15, #21, #68): This is by far the most common electrical issue on HD trucks. Poorly wired trailers, corroded 7-pin connectors, or shorted trailer wires will instantly blow these fuses. What to check first: Inspect the trailer harness and the 7-pin receptacle on the rear bumper for corrosion, water intrusion, or bent pins.
• Auxiliary Power Outlets / Cigar Lighter (Left Dash #23, #24): Plugging in faulty phone chargers, heavy-draw inverters, or air compressors can easily pop these 20-amp fuses. What to check first: Look inside the 12V socket for pennies, paperclips, or debris that might be shorting the contacts.
• A/C Clutch (Under-hood #31): If your air conditioning blows warm, the A/C clutch fuse may have popped. What to check first: Inspect the wiring leading to the A/C compressor for chafing against the engine block or serpentine belt.

Electrical gremlins can sometimes run deeper than a simple blown fuse. If a replacement fuse blows immediately upon installation, you have a direct short to ground that requires professional diagnosis.

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