This procedure covers the removal and replacement of the engine bay fuse box (Battery Junction Box) on the 2021-2024 Ford F-150 with 3.5L EcoBoost V6 engine.

Warnings

Tools required

Parts

• Engine Bay Fuse Box Assembly × 1 — Use OEM Ford BJ3Z-14290-A or equivalent
• Fuse box cover seal (if damaged) × 1 — Use OEM specification

Preparation

1. Park vehicle on level surface and engage parking brake
2. Turn ignition to OFF position and remove key fob from vehicle interior
3. Allow engine to cool completely if recently operated (minimum 30 minutes)
4. Open hood and secure with prop rod
5. Photograph fuse box cover, fuse layout, and all visible wire harness connections for reference
6. Use fuse puller to remove and document all fuses from the fuse box, placing them in labeled containers or diagram

Procedure

1. 1

   Disconnect battery negative terminal
   Locate the battery in the engine bay (driver side near firewall). Using a 10mm socket, loosen the negative (-) terminal bolt. Remove the cable from the battery post and secure it away from the battery to prevent accidental contact. Wait 2 minutes for capacitors to discharge.
   Torque spec

   Battery Terminal Bolts6 Nm (4 lb-ft)
2. 2

   Remove fuse box cover
   The fuse box is located on the driver side fender well near the battery. Press the release tabs on both sides of the fuse box cover and lift upward to remove. Set cover aside in clean location. Inspect cover seal for damage or deterioration.
3. 3

   Document and remove all fuses and relays
   Using the fuse diagram on the cover or in owner's manual, photograph the installed fuse and relay positions. Use fuse puller tool to remove all fuses and relays from the fuse box. Place them in labeled containers matching their positions for reinstallation. Note any blown fuses for replacement.
4. 4

   Disconnect main power cables
   Locate the large power distribution cables connected to the back and bottom of the fuse box. Using an 8mm socket, remove the terminal bolts securing the main battery feed cables and other high-amperage connections. Support heavy cables to prevent strain on connectors. Mark each cable position with tape if not already color-coded.
   ⚠These cables carry high current. Ensure battery is disconnected and cables do not contact each other or ground.
   Torque spec

   Battery Terminal Bolts6 Nm (4 lb-ft)
5. 5

   Release wire harness connectors
   Identify all electrical connectors attached to the fuse box (typically 4-6 multi-pin connectors). Press the release tab on each connector while gently pulling straight away from the fuse box. Do not pull on wires themselves. Some connectors may have secondary locks that must be lifted before the primary release tab will function. Take photos before disconnecting if routing is unclear.
6. 6

   Remove ground straps
   Locate the ground strap(s) attached to the fuse box mounting bracket and vehicle body. Using a 10mm socket, remove the ground strap bolts. Clean the contact surfaces on both the strap terminals and mounting points with a wire brush or electrical contact cleaner to remove any corrosion. This ensures proper grounding when reassembled.
   ℹ️Ground connection quality is critical for proper electrical system operation. Clean all contact surfaces thoroughly.
   Torque spec

   Ground Strap Bolt16 Nm (12 lb-ft)
7. 7

   Remove mounting bracket bolts
   The fuse box is secured to the vehicle with mounting bolts through a bracket assembly. Locate the mounting bolts (typically 2-3 bolts) securing the fuse box bracket to the fender well or body. Using a 10mm socket, remove these mounting bolts. Support the fuse box assembly as you remove the final bolt.
   Torque spec

   Bracket Bolts23 Nm (17 lb-ft)
8. 8

   Remove fuse box assembly
   Carefully lift the fuse box assembly up and away from its mounting location. Guide remaining wire harnesses through any clips or retainers. The assembly may be heavy due to internal relays and bussing. Set the old fuse box on a clean work surface for comparison with the replacement unit.
9. 9

   Prepare replacement fuse box
   Unbox the new fuse box assembly and compare it with the old unit to verify correct part number and connector configurations. Check that all connector ports are clean and free of debris. Do NOT install fuses or relays yet. Apply light coat of dielectric grease to connector seals if operating in harsh environment.
10. 10

    Install new fuse box assembly
    Position the new fuse box into the mounting bracket location. Align the mounting holes with the bracket and fender well mounting points. Guide wire harnesses through their proper routing paths and clips. Hand-start all bracket mounting bolts before tightening.
11. 11

    Torque mounting bracket bolts
    Using a torque wrench with 10mm socket, tighten the bracket mounting bolts in a cross pattern if multiple bolts are present. This ensures even seating of the fuse box assembly. Verify the box sits flush and is not cocked or misaligned.
    Torque spec

    Bracket Bolts23 Nm (17 lb-ft)
12. 12

    Reconnect ground straps
    Install the ground strap(s) to the fuse box mounting bracket and body mounting points. Ensure mating surfaces are clean and make full metal-to-metal contact. Hand-start ground strap bolts, then torque to specification using a torque wrench with 10mm socket.
    Torque spec

    Ground Strap Bolt16 Nm (12 lb-ft)
13. 13

    Reconnect wire harness connectors
    Reconnect all multi-pin electrical connectors to the fuse box in their original positions (reference your photos). Push each connector firmly until you hear and feel a positive click. Verify the release tab engages properly. Engage any secondary connector locks. Ensure no pins are bent or misaligned.
    ⚠Misaligned connector pins will cause electrical faults and may damage circuits. Verify proper alignment before applying force.
14. 14

    Reconnect power cables
    Reconnect the main power distribution cables to their terminals on the fuse box. Ensure each cable lug seats fully on its terminal post. Install terminal bolts and hand-tighten, then torque to specification using an 8mm socket and torque wrench. Verify cables are routed properly and not pinched or stressed.
    Torque spec

    Battery Terminal Bolts6 Nm (4 lb-ft)
15. 15

    Install fuses and relays
    Using your documentation and photos, reinstall all fuses and relays to their correct positions in the new fuse box. Ensure each fuse is fully seated in its slot. Replace any blown fuses identified during removal with correct amperage rating. Do not use higher amperage fuses than specified.
    ⚠️Using incorrect amperage fuses can cause electrical fires or component damage. Always match OEM fuse ratings exactly.
16. 16

    Reinstall fuse box cover
    Inspect the cover seal and replace if damaged or deteriorated. Position the fuse box cover over the fuse box and press down firmly until the retention tabs click into place on both sides. Verify the cover is fully seated and sealed.
17. 17

    Reconnect battery negative terminal
    Clean the battery negative terminal post and cable clamp with wire brush if corroded. Position the negative cable onto the negative battery post and hand-tighten the terminal bolt. Torque the terminal bolt to specification using a 10mm socket and torque wrench. Do not overtighten as this can damage the battery post.
    ⚠Battery terminal bolts require low torque. Overtightening will crack the battery post or terminal clamp.
    Torque spec

    Battery Terminal Bolts6 Nm (4 lb-ft)

Reassembly

1. Double-check that all electrical connectors are fully seated and locked
2. Verify all power cables are torqued and properly routed without pinch points
3. Ensure ground connections are tight and contact surfaces are clean
4. Confirm fuse box cover is fully seated and latched

Verification

• Turn ignition to ON position (do not start engine) and verify instrument cluster illuminates normally
• Check for any warning lights or error messages on instrument cluster
• Verify interior lights, power windows, and radio function properly
• Start engine and let idle for 2 minutes, monitoring for any electrical issues
• Test headlights, turn signals, brake lights, and horn operation
• Verify windshield wipers and HVAC blower function on all speeds
• Check for any unusual smells, smoke, or heat from fuse box area
• Scan for diagnostic trouble codes using OBD-II scanner if available
• Reset clock, radio presets, and driver settings as needed

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