2021 GMC Sierra 1500 Fuse Box Diagram, Amperage & Relay Locations

As an ASE-certified master technician, I’ve spent countless hours tracking down electrical gremlins in modern trucks. The 2021 GMC Sierra 1500 (part of the T1XX platform) is a highly computerized vehicle, heavily reliant on fuses and relays to protect its complex electrical systems. Whether your infotainment screen went black, your trailer brakes aren't engaging, or your 12V outlet stopped charging your phone, knowing exactly where to look can save you an expensive trip to the dealership.

Here is your comprehensive guide to the fuse box locations, amperage ratings, and circuit diagrams for the 2021 GMC Sierra 1500.

Quick Answer: Fuse Box Locations

The 2021 GMC Sierra 1500 features two primary fuse blocks to distribute power throughout the truck:

1. Engine Compartment Fuse Block: Located under the hood on the passenger side, near the battery. It is housed under a black plastic cover secured by tabs.
2. Instrument Panel Fuse Block: Located inside the cabin on the passenger side of the dashboard. You must open the passenger door and remove the side trim panel to access it.

(Note: The Sierra does not have a trunk or cargo area fuse box, though some accessory trailer wiring junctions are located near the rear bumper frame, they are powered from the under-hood block).

Engine Compartment Fuse Block

This main distribution box handles high-draw components, powertrain electronics, exterior lighting, and heavy-duty trailer circuits. To open it, unlatch the tabs on the side of the cover and lift it straight up.

Note: The exact configuration varies slightly depending on your engine (2.7L, 5.3L, 6.2L, or 3.0L Duramax) and trim level. Always verify with the printed legend inside your fuse box lid.

Instrument Panel Fuse Block (Passenger Side)

This fuse box manages the interior electronics, cabin conveniences, safety systems, and body control modules. Remove the side cover of the passenger-side dashboard to access these mini and micro fuses.

How to Test a Fuse

Before you start replacing electrical components, always test the fuse first. It’s the cheapest and most common fix. Here is how I test fuses in the shop:

1. Visual Inspection: Pull the fuse out using a fuse puller (usually found inside the engine fuse box cover) or needle-nose pliers. Look at the U-shaped wire inside the colored plastic. If the wire is broken or there is a black, charred scorch mark, the fuse is blown.
2. Using a Test Light (Fastest Method): Turn the ignition to the "ON" position (do not start the engine). Ground the clip of a 12V automotive test light to a bare metal bolt. Touch the probe to the two tiny metal testing tabs on the top of the fuse while it is still plugged in. If the light turns on for both tabs, the fuse is good. If it only lights up on one side, the fuse is blown.
3. Using a Multimeter: Set your digital multimeter to the "Continuity" or "Ohms" setting. Pull the fuse and touch a probe to each spade of the fuse. If you hear a continuous beep or see a reading close to zero ohms, the fuse is intact. If it reads "OL" (Open Loop), it's blown.

Common Blown Fuses on this Vehicle

In the 2021 GMC Sierra 1500, certain circuits are more prone to popping fuses than others. If you're experiencing issues, check these first:

• 12V Outlets / Cigar Lighter (Instrument Panel F14 & F15): The most frequently blown fuses inside the cabin. Often caused by cheap or faulty phone chargers, or dropping a coin into the open 12V socket. Check the socket for debris before replacing the 20A fuse.
• Trailer Lighting & Brakes (Engine Block F42 & F61): When hooking up to older or poorly wired trailers, a short in the trailer's harness will instantly blow the truck's trailer fuses to protect the Sierra's internal wiring. If you lose trailer lights, always check the trailer wiring for bare copper before replacing the fuse.
• Radio/Infotainment (Instrument Panel F08): If the touchscreen freezes or goes completely black during an over-the-air update or a harsh power cycle, pulling and replacing this 15A fuse can act as a hard reset for the infotainment system.

Important Reminder: Trim variation is common. A Sierra Denali will have a different fuse layout than a base model Work Truck (WT) due to added features like power running boards, premium audio, and advanced driver assistance modules. Never invent or guess fuse numbers and amperages. Always verify with the printed legend inside the fuse box lid, and never replace a blown fuse with one of a higher amperage rating, as this can cause catastrophic wire melting or an electrical fire.

If you keep blowing the same fuse, you have a short circuit that needs professional diagnosis. Find a trusted shop on Repairius.