This procedure covers the replacement of the main power distribution relay in the under-hood fuse box, which controls primary electrical system power distribution.

Warnings

Tools required

Parts

• Main power relay × 1 — Use OEM Ford specification for 3.5L EcoBoost

Preparation

1. Park vehicle on level ground and engage parking brake
2. Turn ignition to OFF position and remove key
3. Allow engine to cool if recently operated
4. Open hood and secure with prop rod
5. Locate battery and engine compartment fuse box

Procedure

1. 1

   Disconnect battery negative terminal
   Using a 10mm socket, loosen the negative battery terminal bolt. Remove the cable from the battery post and secure it away from the battery to prevent accidental contact. Wait at least 2 minutes for capacitors to discharge.
   Torque spec

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

   Access engine compartment fuse box
   Locate the black fuse box on the driver side inner fender near the strut tower. Press the tabs on both sides of the fuse box cover and lift to remove. Set cover aside in a clean location.
3. 3

   Locate main power relay
   Reference the fuse box diagram on the underside of the cover or in the owner's manual. The main relay is typically a larger relay in position R1 or R2. On the 3.5L EcoBoost, it is marked as 'POWER RELAY' and is usually a black or gray high-current relay.
4. 4

   Remove main relay
   Firmly grasp the relay body and pull straight up with steady pressure. The relay is held by friction in the socket. Rock gently side-to-side if needed, but do not bend the terminals. Once removed, inspect the relay socket for corrosion, melting, or damage.
   ⚠Do not force or pry the relay as this can damage socket terminals
5. 5

   Inspect relay socket and terminals
   Examine the socket terminals for signs of heat damage, corrosion, or discoloration. Check for bent pins. If corrosion is present, clean with electrical contact cleaner and a small brush. If socket shows heat damage or melted plastic, the entire fuse box may require replacement.
   ⚠Heat damage to socket indicates excessive current draw and underlying electrical problem that must be diagnosed
6. 6

   Compare old and new relay
   Verify the new relay matches the old relay in physical size, terminal configuration, and markings. Check that part numbers match or that new relay is approved replacement. Note the relay orientation markings on both the relay body and socket.
7. 7

   Install new main relay
   Apply a thin coat of dielectric grease to relay terminals if desired. Align relay terminals with socket, ensuring correct orientation per diagram. Press relay firmly into socket until it seats completely and sits flush with surrounding relays. Verify relay cannot be pulled out easily.
8. 8

   Reinstall fuse box cover
   Position the fuse box cover over the box, aligning the tabs. Press down firmly until you hear or feel the tabs click into place. Verify cover is secure and seated properly around entire perimeter.
9. 9

   Reconnect battery negative terminal
   Clean battery post and cable terminal with wire brush if needed. Place negative cable onto battery post and hand-tighten bolt. Using torque wrench and 10mm socket, tighten battery terminal bolt to specification. Do not overtighten as this can damage battery post.
   ⚠Overtightening battery terminals can crack battery case or damage lead post
   Torque spec

   Battery Terminal Bolts6 Nm (4 lb-ft)

Reassembly

1. Ensure all fuse box covers are properly secured and latched
2. Verify no tools or parts are left in engine compartment
3. Close hood after completing verification steps

Verification

• Turn ignition to ON position (do not start) and verify dashboard lights illuminate normally
• Check for any warning lights or unusual messages on instrument cluster
• Start engine and verify normal operation with no electrical issues
• Test critical electrical systems: headlights, climate control, power windows, radio
• Use multimeter to verify battery voltage shows approximately 14V with engine running (charging system operational)
• Allow vehicle to idle for 2-3 minutes and verify no relay clicking or electrical anomalies
• Turn off engine and verify systems shut down properly

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