2018 Ford F-250 Super Duty Fuse Box Diagram & Amperage

Quick answer

The 2018 Ford F-250 Super Duty has two main fuse box locations: one under the hood in the engine compartment and another inside the cab on the passenger side kick panel. Some configurations may also have a fuse panel in the rear cargo area or under the rear seat, primarily for accessories and trailer towing circuits.

Under-Hood Fuse Box (Battery Junction Box - BJB)

This fuse box is located in the engine compartment, typically near the battery on the driver's side. It houses high-current fuses for major electrical components and relays for various systems.

Common Relays in the Under-Hood Fuse Box:

• R1: Fuel Pump Relay
• R2: Starter Relay
• R3: PCM Relay
• R4: A/C Clutch Relay
• R5: Blower Motor Relay
• R6: Headlight Relays (often separate for low/high beams)
• R7: Trailer Tow Park Lamp Relay

Note: Fuse and relay locations may vary slightly based on specific trim levels and optional equipment. Always refer to the fuse legend inside the fuse box lid for the most accurate information for your vehicle.

Passenger Compartment Fuse Box (Smart Junction Box - SJB)

This fuse box is located inside the cabin, typically behind the kick panel on the passenger side. It controls many interior electrical components and accessories.

Note: As with the under-hood fuse box, verify the printed legend on the fuse box cover for the exact layout and circuit descriptions for your specific vehicle configuration.

How to test a fuse

Testing a fuse is a straightforward process that can help you diagnose electrical issues. Here's how to do it:

1. Safety First: Turn off the ignition and remove the key. For under-hood fuses, disconnect the negative battery terminal if working with high-amperage fuses or relays.
2. Locate the Fuse: Refer to your vehicle's owner's manual or the fuse box lid diagram to find the suspected fuse.
3. Visual Inspection: Carefully pull the fuse straight out using a fuse puller (usually included in the fuse box or tool kit). Hold it up to the light. A good fuse will have a continuous wire or metal strip inside. If it's broken or melted, the fuse is blown.
4. Using a Multimeter (for a more accurate test):
   • Set your multimeter to the continuity setting (often indicated by a speaker icon). If it doesn't have continuity, use the ohms setting (Ω).
   • Touch the probes of the multimeter to the exposed metal test points on the top of the fuse (or the metal blades if using an older style fuse). You don't need to remove the fuse from the box for this step if it has test points.
   • If the multimeter beeps or shows a reading of