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GM Tech (Cam)
GM Tech (Cam), GMC Mechanic
Category: GM
Satisfied Customers: 29534
Experience:  GM Grand Master Technician 2007. 14 years experience.
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2003 GMC Envoy: The 3rd tail light on the back hatch..brake lights

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I recently purchased a 2003 GMC Envoy XL. The 3rd tail light on the back hatch doesn't burn. The other brake lights seem to be fine. Are the bulbs able to be replaced in the 3rd light or do we need to replace the whole assembly? If there is a bulb only to check/change, what is the best way to get to it?

Welcome to Just Answer and thank you for asking your question. I look forward to helping you fix your vehicle.


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Please feel free to reply as needed.


This CHMSL is a tube so it is likely faulty. Below are replacement instructions.

Object Number: 721363  Size: SH

  • Open the liftgate.
  • Lower the rear portion of the headliner by releasing the 2 headliner retaining pins.
  • Disconnect the high mount stoplamp electrical connector (2).
  • Remove the grommet (1) from the body
  • Notice: Do NOT raise the liftgate while the liftgate glass is open. This can result in damage to the high-mounted stoplamp, the liftgate hinges, or the liftgate glass.

  • Close the liftgate.
  • Open the liftgate window.

  • Object Number: 732876  Size: SH

  • Remove the 2 screws that retain the high mount stoplamp to the lift gate window reveal molding.
  • Remove the high mount stoplamp from the vehicle.
  • Customer: replied 7 years ago.
    So is the CHMSL the bulb, or the entire power assembly for this light? Is this something that can be purchased at the parts store if bad, or is this typically a dealer's item only?

    This is a dealer only item.

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