This procedure covers the removal and replacement of the horn relay in the under-hood fuse/relay box on a 2021-2024 Ford F-150 with the 3.5L EcoBoost V6 engine.

Warnings

Tools required

Parts

• Horn relay × 1 — Motorcraft SW-7157 or equivalent

Preparation

1. Park vehicle on level surface and engage parking brake
2. Turn ignition off and remove key fob from vehicle
3. Allow engine to cool if recently operated
4. Open hood and secure with prop rod

Procedure

1. 1

   Disconnect battery negative terminal
   Locate the battery in the engine bay. Using a 10mm socket, loosen and remove the negative (-) terminal bolt. Carefully lift the negative cable away from the battery post and position it where it cannot accidentally contact the terminal. Wait at least 2 minutes for electrical systems to discharge.
   Torque spec

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

   Locate the under-hood fuse/relay box
   The primary fuse/relay box is located on the driver's side of the engine bay, mounted to the inner fender near the firewall. It is a black rectangular box with a cover labeled with fuse and relay positions.
3. 3

   Remove fuse box cover
   Release the cover retention tabs by pressing down and outward on each side of the cover. Lift the cover away from the fuse box. The underside of the cover contains a diagram showing relay and fuse locations.
4. 4

   Identify the horn relay
   Using the diagram on the fuse box cover or the label inside the box, locate the horn relay. It is typically labeled as 'HORN' or relay position R2.6. The horn relay is a small cube-shaped component with four blade terminals plugging into the relay socket.
5. 5

   Remove the old horn relay
   Firmly grasp the horn relay between thumb and forefinger. Pull straight upward with steady pressure to extract the relay from its socket. The relay should release from the socket with moderate force. If difficult to remove, gently rock the relay side-to-side while pulling upward. Inspect the relay terminals and socket for corrosion or damage.
6. 6

   Inspect relay socket
   Examine the relay socket for any signs of heat damage, corrosion, or bent pins. If corrosion is present on socket terminals, carefully clean with electrical contact cleaner and allow to dry completely. Ensure all four socket terminals are present and properly seated.
7. 7

   Install new horn relay
   Orient the new horn relay to match the socket configuration - the relay will only fit one way due to the blade terminal arrangement. Align the relay terminals with the socket and press firmly downward until the relay is fully seated and flush with surrounding relays. The relay should click into place when properly installed.
8. 8

   Reinstall fuse box cover
   Position the fuse box cover over the relay box, ensuring it is oriented correctly with the diagram visible on top. Press down firmly on all edges until the retention tabs engage with audible clicks on both sides.
9. 9

   Reconnect battery negative terminal
   Position the negative battery cable terminal over the negative battery post. Install the terminal bolt and tighten to specification using a torque wrench. Ensure the connection is secure but do not overtighten as this can damage the battery post or terminal.
   ⚠Do not overtighten battery terminal - use torque wrench to prevent damage to battery post
   Torque spec

   Battery Terminal Bolts6 Nm (4 lb-ft)

Reassembly

1. Ensure fuse box cover is fully secured with all retention tabs engaged
2. Verify battery cable is tight and properly positioned away from moving components
3. Close hood and verify it latches securely

Verification

• Turn ignition to ON position without starting engine
• Press the horn button on the steering wheel - horn should sound immediately
• Test both sides of the horn button if equipped with dual horn switches
• If horn does not function, verify relay is fully seated and check horn fuse
• Reset clock and radio presets as needed

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