Replace or repair the third brake light (center high-mounted stop lamp) assembly on the rear cab of a 2021-2024 Ford F-150.

Warnings

Tools required

Parts

• Third brake light assembly (CHMSL) × 1 — Use OEM Ford part number or equivalent LED assembly

Preparation

1. Park vehicle on level surface and engage parking brake
2. Turn ignition off and remove key from vehicle
3. Open hood and disconnect battery negative terminal to prevent electrical shorts
4. Wait 2 minutes after battery disconnection for system discharge
5. Clean the area around the third brake light to prevent debris from entering the cab during removal

Procedure

1. 1

   Access third brake light from inside cab
   Open the rear window of the cab. The third brake light assembly is accessed from inside the cab, above the rear window. You will need to work from the rear seat area with the rear window open or removed for easier access.
2. 2

   Remove interior trim cover
   Locate the interior trim cover that conceals the third brake light mounting area. This is typically located on the headliner at the rear of the cab. Use a plastic trim tool to carefully pry down the trim cover, starting from one side. The cover is held by plastic clips. Work gently to avoid breaking the clips or damaging the headliner material.
3. 3

   Disconnect electrical connector
   Locate the electrical connector attached to the back of the third brake light assembly. Press the locking tab on the connector and pull it straight away from the light assembly. Do not pull on the wires themselves. If the connector is difficult to access, you may need to partially lower the assembly first.
4. 4

   Remove mounting fasteners
   Using a T20 Torx driver, remove the two or three Torx screws that secure the third brake light assembly to the cab. These screws typically thread into the sheet metal of the cab roof. Keep track of these screws as they are specific to this application. Support the light assembly with one hand as you remove the final screw to prevent it from falling.
5. 5

   Remove third brake light assembly
   Carefully pull the third brake light assembly away from the cab exterior. The assembly may have a gasket or seal that creates some resistance. Work the assembly free gently, being careful not to damage the gasket (which should be reused if in good condition) or the paint around the mounting area. Bring the assembly inside the cab through the access area.
6. 6

   Inspect and clean mounting area
   Inspect the mounting surface on the cab for any corrosion, damage, or debris. Clean the mounting surface with isopropyl alcohol and a microfiber cloth. Inspect the gasket or seal (if equipped) for damage, cracking, or deterioration. The gasket must seal properly to prevent water intrusion. Replace the gasket if it shows any signs of wear.
7. 7

   Prepare new third brake light assembly
   Remove the new third brake light assembly from its packaging. If a new gasket is included, install it onto the back of the new light assembly, ensuring it is properly seated in the gasket channel. Verify that the new assembly matches the original in terms of connector type and mounting hole locations.
8. 8

   Install new assembly
   Position the new third brake light assembly from inside the cab, guiding it through the access area and aligning the mounting holes with the holes in the cab. Ensure the gasket is properly positioned to seal against the cab exterior. From inside, start all mounting screws by hand to ensure proper thread engagement before tightening any of them.
9. 9

   Tighten mounting fasteners
   Using the T20 Torx driver, tighten the mounting screws in a cross pattern (if three screws) or alternating pattern (if two screws) to ensure even pressure on the gasket. Tighten screws snugly but do not overtighten, as this can crack the light assembly housing or strip the threads in the sheet metal. Approximate torque is 12-15 in-lb (hand-tight plus 1/4 turn).
10. 10

    Reconnect electrical connector
    Connect the electrical connector to the back of the new third brake light assembly. Push the connector straight into the socket until you hear or feel a positive click, indicating the locking tab has engaged. Gently tug on the connector to verify it is fully locked in place.
11. 11

    Reinstall interior trim cover
    Position the interior trim cover back into place over the third brake light mounting area. Align the plastic clips with their receptacles in the headliner structure. Press firmly on the trim cover at each clip location until you hear or feel each clip snap into place. Ensure the cover sits flush with the surrounding headliner.
12. 12

    Reconnect battery and test
    Reconnect the battery negative terminal. Have an assistant observe the third brake light from outside the vehicle while you press the brake pedal with the ignition in the ON position. Verify the third brake light illuminates brightly and evenly. Test multiple times to ensure reliable operation.
    ⚠️Do not operate vehicle on public roads until proper third brake light function is verified. Non-functional brake lights significantly increase rear-end collision risk.
    Torque spec

    Battery Terminal Bolts6 Nm (4 lb-ft)

Reassembly

1. Ensure all interior trim pieces are securely clipped and flush with surrounding surfaces
2. Verify no tools or fasteners were left in the headliner area
3. Close rear window if it was opened during the procedure

Verification

• With ignition ON, press brake pedal and verify third brake light illuminates brightly
• Have assistant verify light is visible from at least 500 feet behind vehicle in daylight conditions
• Check for any water leaks around the third brake light after the next car wash or rain
• Verify no warning lights or messages appear on the instrument cluster related to brake lights
• Confirm interior trim cover is secure and does not rattle while driving

More procedures for this vehicle