Third Brake light CHSML not working
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Thread: Third Brake light CHSML not working

  1. #1
    FRESHMAN ROVER
    Join Date
    October 20th, 2009
    Location
    Los Angeles, CA
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    18

    Third Brake light CHSML not working

    Okay guys, so I've had my new to me RR for about a week and noticed that my third brake light is not working. I've searched for others with this issue, but didn't find what I was looking for. I thought the diagnostics would tell me if the bulbs/LEDs were not working but I dont get any failure message, is there somehting I'm missing?
    2004 Range Rover, Lux, Silver on Gray, all stock for now!

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  3. #2
    Premium Member
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    December 28th, 2005
    Location
    Kilkhampton, Cornwall, UK
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    1,985

    Re: Third Brake light CHSML not working

    Are there any signs that the rear window surround has been off? The rear wipers can cause probs so if someones been in there to fix that then maybe they unplugged the light and forgot to plug it back in? I think you also need to get in there with a multimeter to see if it's getting power, or whether its the bulbs that have failed. Although unlikely its all of them, it could be something nice and easy.

    D
    1999 4.6 HSE Blenheim Silver

  4. #3
    FRESHMAN ROVER
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    October 20th, 2009
    Location
    Los Angeles, CA
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    Re: Third Brake light CHSML not working

    Good point, I did notice that the surround did look a little loose so I snapped it back in but I thought that was from being slammed shut too many times. I'll check the voltage with a MM, but does that failure show up on the message center if the LEDs are out for some reason? Are they LEDs or are they incandescents meant to look like LEDs?
    2004 Range Rover, Lux, Silver on Gray, all stock for now!

  5. #4
    FRESHMAN ROVER
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    October 20th, 2009
    Location
    Los Angeles, CA
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    Re: Third Brake light CHSML not working

    Well I finally got a chance to take a look at this issue closer. I removed the surround and found the connector that runs up to the CHMSL (brake light). I used my MM and everything leading up to the light tested fine, 13 VDC with the brake pedal depressed. I removed the body panel that the light is mounted to so I could take it apart to find out what was wrong. After removing the housing from the panel (body) I quickly realized that this unit was not serviceable. It's an ultrasonically welded assembly; lens to housing. I figured since I was going to have to replace it anyway, I'll take it apart and learn a little something. I put it in the freezer to make the joint brittle so it would be easier to take apart. After 30 minutes in the freezer the pieces came apart pretty easy with the help of a flat screwdriver. Two long circuit boards with LED's, resistors, and a diode is what you will find inside. I proceeded to test all the components with my dc power supply set to 6vdc. All the LED's were fine, but the diode had to be removed to test. Once I removed the diode and tested it, I realized that was the failure point. The diode (rectifier) was bad (1N4003). And after replacing it....waala, everything works! With the help of some 5min epoxy and silicone to seal up the seam it's back on the truck and looks good (patting myself on back).
    I would have taken pictures, but I realized that after the fact. Not to mention it didn't really seem like a common issue.
    2004 Range Rover, Lux, Silver on Gray, all stock for now!

  6. #5
    SENIOR ROVER
    Join Date
    September 11th, 2009
    Location
    Chilterns
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    1,122

    Re: Third Brake light CHSML not working

    Quote Originally Posted by powerfiend
    Well I finally got a chance to take a look at this issue closer. I removed the surround and found the connector that runs up to the CHMSL (brake light). I used my MM and everything leading up to the light tested fine, 13 VDC with the brake pedal depressed. I removed the body panel that the light is mounted to so I could take it apart to find out what was wrong. After removing the housing from the panel (body) I quickly realized that this unit was not serviceable. It's an ultrasonically welded assembly; lens to housing. I figured since I was going to have to replace it anyway, I'll take it apart and learn a little something. I put it in the freezer to make the joint brittle so it would be easier to take apart. After 30 minutes in the freezer the pieces came apart pretty easy with the help of a flat screwdriver. Two long circuit boards with LED's, resistors, and a diode is what you will find inside. I proceeded to test all the components with my dc power supply set to 6vdc. All the LED's were fine, but the diode had to be removed to test. Once I removed the diode and tested it, I realized that was the failure point. The diode (rectifier) was bad (1N4003). And after replacing it....waala, everything works! With the help of some 5min epoxy and silicone to seal up the seam it's back on the truck and looks good (patting myself on back).
    I would have taken pictures, but I realized that after the fact. Not to mention it didn't really seem like a common issue.
    Five gold stars for what can only be described as an excellent job done and great story too.

  7. #6
    SGW
    SGW is offline
    FRESHMAN ROVER
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    September 29th, 2007
    Location
    Headcorn Kent UK
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    238

    Re: Third Brake light CHSML not working

    Nice piece of information, I like the freezer trick!
    Stewart.
    Owned first RR in 1978 had 5 since. Present one's 2002 Giverny Green Vogue and 2002 Giverny Green HSE both 4.4 LPG.

  8. #7
    NEWBIE
    Join Date
    August 4th, 2012
    Location
    United States
    Posts
    1

    Re: Third Brake light CHSML not working

    how do i remove the third brake light on my 03 rr hse?
    Keith

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