Replace the center high-mounted stop lamp (CHMSL/third brake light) assembly located on the rear cab wall of the F-150.

Warnings

Tools required

Parts

• Third brake light assembly (CHMSL) × 1 — Use OEM Ford specification for proper fit and sealing
• Foam seal/gasket (if not included with new light) × 1 — Usually included with OEM assembly

Preparation

1. Park vehicle on level surface and engage parking brake
2. Turn ignition to OFF position and remove key
3. Lower tailgate to improve access to rear cab wall
4. Clean the area around the third brake light to prevent dirt from entering the cab during removal

Procedure

1. 1

   Access interior mounting points
   From inside the cab, carefully pull down or remove the headliner trim at the rear window if necessary. On most 2011-2014 F-150 models, you can access the mounting hardware by gently pulling the headliner away from the rear window area without full removal. The third brake light is mounted from the exterior but secured with nuts accessible from inside.
2. 2

   Disconnect electrical connector
   Locate the wiring harness connector attached to the back of the third brake light assembly from inside the cab. Press the tab on the connector and pull straight out to disconnect. Note the connector orientation for reassembly.
3. 3

   Remove interior mounting fasteners
   Remove the mounting nuts or screws securing the third brake light assembly from inside the cab. Typically there are 2-4 fasteners depending on the specific configuration. Keep these fasteners organized as they may be reused if in good condition.
   ℹ️Have a helper support the light assembly from the outside while removing the last fastener to prevent it from falling.
4. 4

   Remove light assembly from exterior
   From outside the vehicle at the rear cab wall, carefully pull the third brake light assembly away from the mounting surface. The assembly should separate once all fasteners are removed. If stuck, gently use a flathead screwdriver or trim tool to break the seal, being careful not to damage the paint or mounting surface.
5. 5

   Inspect and clean mounting surface
   Inspect the mounting area on the cab for any damage, corrosion, or old gasket material. Clean the surface thoroughly with a clean cloth. Check the mounting holes for any cracks or damage. Verify the new third brake light assembly includes a fresh foam gasket/seal.
6. 6

   Install new light assembly
   Position the new third brake light assembly with the foam gasket properly aligned to the mounting surface on the exterior cab wall. Ensure the electrical connector portion extends into the cab area and the mounting studs or holes align correctly. Press firmly to seat the gasket.
7. 7

   Secure mounting fasteners
   From inside the cab, thread on the mounting nuts or screws by hand onto the studs or into the mounting holes. Tighten in a cross-pattern if multiple fasteners are present to ensure even compression of the gasket seal. Use care not to overtighten plastic components. If using Cover Screws (metal fasteners), torque to specification.
   ⚠Do not overtighten fasteners on plastic housings as this can crack the assembly. Snug is sufficient for plastic-threaded applications.
   Torque spec

   Cover Screws14 Nm (10 lb-ft)
8. 8

   Reconnect electrical connector
   Connect the wiring harness to the new third brake light assembly, ensuring the connector clicks securely into place. Verify the connection is fully seated and the locking tab engages.
9. 9

   Test light operation
   Turn the ignition to the ON position (engine does not need to run). Have a helper press the brake pedal while you verify the third brake light illuminates properly. Check for full brightness and that all LED elements or bulbs light up. Also verify the light turns off when the brake pedal is released.
10. 10

    Check for water leaks and alignment
    Inspect the exterior installation to ensure the light assembly is flush with the cab wall and the gasket seal is properly compressed around the entire perimeter. Check that no gaps exist that could allow water intrusion. Verify proper alignment from multiple angles.

Reassembly

1. Reinstall or reposition the headliner trim at the rear window area, ensuring it sits properly
2. Close the tailgate and verify it does not contact the third brake light assembly
3. Clean any fingerprints or marks from the new light lens with a microfiber cloth

Verification

• With ignition ON, press the brake pedal and verify the third brake light illuminates brightly
• Confirm all LED elements or bulb sections illuminate evenly
• Check that the light turns off completely when the brake pedal is released
• Verify no warning lights appear on the instrument cluster related to brake lights
• Inspect the exterior seal for proper seating with no visible gaps
• Test drive the vehicle in a safe area and have a follower verify brake light operation during actual braking
• After the first rain or car wash, inspect for any water leaks into the cab around the mounting area

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