This procedure covers the replacement of a generic relay in the engine compartment or under-hood fuse box on a 2021-2024 Ford F-150 with the 3.5L EcoBoost engine.

Warnings

Tools required

Parts

• Replacement relay × 1 — Use OEM specification matching existing relay amperage and type

Preparation

1. Park vehicle on level surface and engage parking brake
2. Turn ignition off and remove key
3. Allow engine to cool if recently operated
4. Locate the relay to be replaced - refer to fuse box diagram on underside of fuse box cover or owner's manual
5. Identify the relay type and amperage rating for replacement part ordering

Procedure

1. 1

   Disconnect negative battery terminal
   Loosen and remove the negative battery terminal cable from the battery. Move cable aside to prevent accidental contact. This prevents electrical shorts during relay replacement.
   Torque spec

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

   Access relay location
   Locate the fuse/relay box containing the target relay. On the 2021-2024 F-150, the main under-hood fuse box is located on the passenger side of the engine compartment near the firewall. If relay is in cabin fuse box, locate panel under driver's side dash.
3. 3

   Remove fuse box cover
   Release the cover retaining tabs by pressing or pulling as designed. Some covers use screws - remove these if present and set aside. Lift cover away to expose relays and fuses.
   Torque spec

   Cover Screws12 Nm (9 lb-ft)
4. 4

   Identify target relay
   Use the diagram on the fuse box cover or in the owner's manual to identify the exact relay position. Verify relay number matches the circuit requiring service. Note the relay orientation and terminal configuration before removal.
5. 5

   Remove failed relay
   Grasp the relay firmly and pull straight up with steady pressure to extract from socket. If relay is difficult to remove, use a relay puller tool or carefully use needle-nose pliers to grip the relay body (not terminals). Rock gently side to side while pulling if needed.
6. 6

   Inspect relay socket
   Examine the relay socket terminals for corrosion, burning, or damage. Check for melted plastic or discoloration indicating overheating. If socket is damaged, the entire fuse box may require replacement. Clean any minor corrosion with electrical contact cleaner.
7. 7

   Install new relay
   Verify new relay matches original specifications including amperage rating and terminal configuration. Align relay pins with socket terminals, ensuring correct orientation. Press relay firmly into socket until fully seated and flush with surrounding relays. Do not force - if resistance is felt, check alignment.
8. 8

   Reinstall fuse box cover
   Position cover over fuse box and ensure all tabs align properly. Press down firmly to engage retaining clips. If cover uses screws, install and tighten to specification.
   Torque spec

   Cover Screws12 Nm (9 lb-ft)
9. 9

   Reconnect battery
   Reinstall negative battery terminal cable to battery post. Ensure clean contact between terminal and post. Tighten terminal bolt to specification - do not overtighten as this can damage the battery post.
   Torque spec

   Battery Terminal Bolts6 Nm (4 lb-ft)

Reassembly

1. Ensure fuse box cover is fully seated and all retaining tabs are engaged
2. Verify battery terminal is secure and cannot be moved by hand

Verification

• Turn ignition to ON position without starting engine - verify dashboard warning lights function normally
• Operate the system controlled by the replaced relay to confirm proper function
• Start engine and verify relay-controlled component operates as designed
• Check for any new warning lights or diagnostic codes
• Reset clock and radio presets as needed

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