Third Brake Light

This procedure covers the removal and replacement of the third brake light (center high-mounted stop lamp/CHMSL) assembly on 2015-2020 Ford F-150 trucks.

Warnings

Tools required

Parts

• Third brake light assembly (CHMSL) × 1 — Use OEM specification or aftermarket equivalent
• Replacement mounting clips (if damaged) × 1 — Use OEM specification

Preparation

1. Park vehicle on level surface and engage parking brake
2. Turn ignition off and remove key
3. Allow any recently-used lights to cool for 5 minutes
4. Lower tailgate for easier access to rear cab panel area
5. Determine your specific third brake light mounting configuration (standard cab-mounted or cargo management system-integrated)

Procedure

1. 1

   Access the third brake light assembly
   From inside the cab, locate the third brake light assembly at the top center of the rear window/cab. If your truck has a sliding rear window, slide it open to access the interior mounting area. On standard installations, the light is accessed from inside the cab beneath a trim cover.
2. 2

   Remove interior trim cover (if applicable)
   Using a flathead screwdriver or trim removal tool, carefully pry down the interior trim cover that conceals the brake light mounting hardware. The cover typically has clips on each side. Work gently to avoid breaking the clips. Set the cover aside in a safe location.
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. Note the orientation of the connector for reinstallation.
   ⚠Do not pull on the wires themselves. Always grip the connector body to prevent wire damage.
4. 4

   Remove mounting fasteners
   Remove the mounting screws or nuts securing the third brake light assembly to the cab. Typical installations use 2-4 fasteners. Support the light assembly from the exterior side while removing the final fastener to prevent it from falling.
5. 5

   Remove brake light assembly
   Carefully pull the third brake light assembly away from the mounting surface. On some models, the assembly may have a gasket or seal that provides slight resistance. Inspect the mounting area and gasket for damage or debris.
6. 6

   Prepare new assembly
   Inspect the new third brake light assembly and verify it matches the original. Transfer the gasket or seal to the new assembly if it's reusable and in good condition, or use the new gasket provided. Ensure the mounting surface on the cab is clean and free of old adhesive or debris.
7. 7

   Install new brake light assembly
   Position the new third brake light assembly into the mounting location from the exterior, ensuring the gasket seats properly. Align the mounting holes with the fastener locations. Have an assistant support the assembly from outside while you work from inside, if possible.
8. 8

   Secure mounting fasteners
   Install and hand-tighten all mounting fasteners. Tighten fasteners in a cross-pattern to ensure even pressure on the gasket and prevent stress cracks in the lens. Do not overtighten plastic-mounted assemblies. If fasteners are specified to be torqued, follow manufacturer specifications.
9. 9

   Connect electrical connector
   Reconnect the electrical connector to the new third brake light assembly. Push firmly until you hear or feel the locking tab click into place. Gently tug on the connector to verify it's securely locked.
10. 10

    Reinstall interior trim cover
    Position the interior trim cover back into place and press firmly on the clip locations until each clip snaps securely into position. Verify the cover is flush and seated properly around its entire perimeter.
11. 11

    Test brake light operation
    Turn the ignition to the ON position (engine does not need to run). Have an assistant press the brake pedal while you verify the third brake light illuminates. The light should be bright and uniform across the entire lens. Also verify the side brake lights still function properly.
    ⚠️Do not operate the vehicle on public roads until you have verified all brake lights function correctly. Inoperative brake lights create a serious collision hazard.

Reassembly

1. Ensure all trim pieces are securely fastened and properly aligned
2. Close sliding rear window if it was opened during the procedure
3. Raise tailgate and verify it operates normally without interference from the new assembly

Verification

• With ignition ON, have an assistant press and release the brake pedal multiple times while you observe all three brake light assemblies (left, right, and center third brake light) illuminate and extinguish
• Verify the third brake light illuminates with the same brightness as before and shows no flickering or dim spots
• Check that no warning lights appear on the instrument cluster related to brake light failure
• Inspect the exterior of the assembly for proper sealing and alignment with no gaps in the gasket
• Perform a short test drive in a safe area and verify brake lights function during actual braking before returning to normal operation

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