Third Brake Light

Replace or repair the center high-mounted stop lamp (CHMSL) third brake light assembly on the rear cab of a 1994-2007 Dodge Ram 2500.

Warnings

Tools required

Parts

• Third brake light assembly (CHMSL) × 1 — Use OEM Mopar or equivalent LED/incandescent unit for model year
• Replacement bulbs (if assembly uses bulbs) × 2 — 921 or 912 wedge bulb typical, verify for your year
• Mounting gasket or seal × 1 — Often included with new light assembly

Preparation

1. Park vehicle on level surface and engage parking brake
2. Turn ignition off and remove key
3. Disconnect negative battery terminal to de-energize brake light circuit and prevent electrical shorts
4. Allow any recently-used brake lights to cool for 5 minutes
5. If cab has a headliner, you may need to access the assembly from inside the cab (extended cab/quad cab models) or from exterior only (regular cab)
6. Identify your third brake light configuration: roof-mounted on cab or mounted in rear sliding window frame (if equipped)
7. Gather replacement parts and verify correct part number for your specific model year

Procedure

1. 1

   Access the third brake light assembly
   The third brake light on these Dodge Ram trucks is roof-mounted at the top rear edge of the cab and is accessed from the exterior. Work from outside on a stable platform (such as a step stool or the tailgate area) if necessary to reach the roof-mounted light safely.
2. 2

   Remove the light lens or cover
   Locate the Phillips head screws or fasteners securing the lens cover to the housing base (typically 2-4 screws). Remove screws carefully and set aside. On some models, the entire assembly is one piece and this step does not apply. Gently pull the lens away from the housing, being careful not to damage the gasket seal. If bulbs are accessible and only bulb replacement is needed, proceed to bulb replacement; otherwise continue to remove entire assembly.
3. 3

   Disconnect electrical connector
   Locate the electrical connector feeding the third brake light. Press the release tab and pull the connector apart. If the connector is corroded or difficult to separate, spray with electrical contact cleaner and gently work it free. Do not pull on wires directly. Note the connector orientation for reassembly.
4. 4

   Remove mounting fasteners
   Remove the Phillips head screws or bolts securing the light assembly base to the cab roof or window frame. Typical installations use 2-4 mounting screws. Keep track of any washers or spacers. Note the location of the rubber gasket or seal that prevents water intrusion.
5. 5

   Remove the third brake light assembly
   Carefully lift the assembly away from the mounting surface. Feed the wire harness through the mounting hole as you remove the assembly. Inspect the mounting area for rust, corrosion, or damage to the cab roof. Check the condition of the rubber gasket seal.
6. 6

   Inspect and clean mounting surfaces
   Clean the mounting surface on the cab roof or window frame with a clean cloth. Remove any old gasket material, dirt, or corrosion. Ensure the mounting holes are clean and free of debris. Clean the electrical connector pins with electrical contact cleaner if corrosion is present. Apply a small amount of dielectric grease to connector terminals to prevent future corrosion.
7. 7

   Prepare new or serviced assembly
   If replacing bulbs in existing assembly: remove old bulbs by pulling straight out from socket, insert new bulbs by pushing straight in until seated. If installing new assembly: verify it matches the original configuration and includes mounting gasket. Position the gasket seal on the new assembly base, ensuring it is properly seated in the gasket channel.
8. 8

   Install the light assembly
   Feed the wire harness through the mounting hole from the exterior. Position the assembly on the mounting surface, aligning the screw holes and ensuring the gasket seal is properly positioned to prevent water leaks. The assembly should sit flush against the mounting surface without gaps.
9. 9

   Install mounting fasteners
   Start all mounting screws by hand to ensure proper thread engagement. Tighten screws in a crossing pattern (opposite corners) to evenly compress the gasket seal. If screws are threaded into sheet metal, snug them lightly. Tighten gradually and do not overtighten, as the plastic housing can crack or the thin cab roof can dimple. Snug only - approximately 2.0-2.5 Nm (18-22 lb-in) is sufficient for these small screws.
10. 10

    Connect electrical connector
    Align the electrical connector and push together firmly until the locking tab clicks into place. Gently tug on the connector to verify it is fully locked. Ensure the wiring is routed properly and not pinched or stressed.
11. 11

    Install lens cover (if applicable)
    If your assembly has a removable lens cover, position it over the housing and align screw holes. Install lens screws and tighten in a crossing pattern. Do not overtighten plastic lens screws - snug is sufficient, approximately 2-3 Nm (18-26 lb-in) by feel, just until the lens is secure against the gasket.
12. 12

    Reconnect battery and test
    Reconnect the negative battery terminal and tighten the clamp nut to specification (approximately 5-8 Nm / 45-70 lb-in). Turn the ignition to ON position (engine does not need to run). Have an assistant press the brake pedal while you verify the third brake light illuminates fully and brightly. Check for proper sealing and no light bleeding around gasket. Test multiple times to ensure consistent operation.
    Torque spec

    Battery Terminal Bolts6 Nm (4 lb-ft)

Reassembly

1. Ensure all mounting screws are torqued properly to prevent water leaks but avoid overtightening plastic and thin sheet metal
2. Verify the rubber gasket seal is properly compressed around the entire perimeter of the assembly
3. Check that wiring is not pinched and connector is fully locked
4. If you removed interior trim panels or headliner, reinstall according to original configuration

Verification

• With ignition ON, have an assistant press and hold the brake pedal while you observe the third brake light from behind the vehicle - all bulbs or LED segments should illuminate brightly
• Release brake pedal and verify light turns off completely with no dim glow
• Cycle brake pedal 10-15 times and verify consistent operation
• Check for water leaks during the next car wash or rain - no water should enter the cab around the light assembly
• Verify all other brake lights (tail lights) still function normally
• Test drive in safe area and verify brake lights work during actual braking
• CRITICAL: Do not operate vehicle on public roads until third brake light function is verified - this is a required safety device

Related trouble codes on this vehicle

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