This procedure covers the replacement of the main power distribution relay (also called the battery junction box relay) in a 2015-2020 Ford F-150 with 5.0L V8 Coyote engine.

Warnings

Tools required

Parts

• Main power distribution relay × 1 — Use OEM Ford relay or Motorcraft SW-10161

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 driven
4. Gather all tools and the replacement relay
5. Open hood and secure with prop rod

Procedure

1. 1

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

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

   Locate the battery junction box
   The battery junction box (main fuse/relay box) is located on the driver's side fender near the battery. It is a black rectangular box with multiple connectors on top and bottom. Identify the main relay location by consulting the diagram on the underside of the junction box cover.
3. 3

   Remove junction box cover
   Press the two release tabs on the sides of the junction box cover and lift upward to remove. Set the cover aside in a clean location. Note the relay diagram printed on the underside of the cover for reference.
4. 4

   Identify the main relay
   Locate the main power distribution relay in the junction box. On 2015-2020 F-150 models, this is typically a large rectangular relay in the upper section of the box, often labeled 'Main' or with relay number R18. Verify identification using the cover diagram.
5. 5

   Remove the failed relay
   Grasp the relay firmly and pull straight upward with steady pressure to remove it from the socket. If the relay is stuck, use a small flathead screwdriver to gently pry upward on alternating sides while pulling. Do not rock the relay side to side excessively as this can damage the socket terminals.
   ⚠Do not force the relay or use excessive prying force as the socket terminals are fragile
6. 6

   Inspect relay socket
   Examine the relay socket terminals for signs of corrosion, discoloration, or damage. If corrosion is present, clean the terminals gently with a wire brush or fine sandpaper. Check that all socket terminals are straight and not bent. Apply a small amount of dielectric grease to the socket terminals if desired.
7. 7

   Install new relay
   Verify the new relay matches the old relay in size, pin configuration, and markings. Align the relay pins with the socket terminals, ensuring correct orientation (there will be a guide or keying feature). Push the relay firmly into the socket until it seats completely and sits flush with the junction box mounting surface.
   ⚠Ensure relay is oriented correctly before applying pressure to avoid bending socket pins
8. 8

   Reinstall junction box cover
   Position the junction box cover over the box and press down firmly until both side tabs click into place. Ensure the cover is fully seated and secure.
9. 9

   Reconnect battery negative terminal
   Place the negative battery cable back onto the negative battery post. Install the terminal bolt and tighten to specification using a torque wrench. Ensure the connection is snug but do not overtighten to avoid damaging the battery post.
   Torque spec

   Battery Terminal Bolts6 Nm (4 lb-ft)

Reassembly

1. Double-check that the junction box cover is properly secured
2. Ensure no tools or parts are left in the engine compartment
3. Reset clock and radio presets as needed

Verification

• Turn ignition to ON position (do not start engine) and verify dashboard lights illuminate normally
• Check for any electrical warning lights or fault messages on the instrument cluster
• Start the engine and verify it cranks and starts normally
• Test electrical accessories (lights, windows, wipers) to ensure proper operation
• If issues persist, verify correct relay was installed and is fully seated in socket

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