Marker Lights Dimming

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by OhNoTerry, Mar 26, 2025.

  1. OhNoTerry

    OhNoTerry Medium Load Member

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    May 22, 2021
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    Long story short I swapped all of my lights over to amber/purple Trux LED lights. Well I’ll randomly have a light either completely go out, or dim. Right now one of my lights dimmed out on me, I swapped the whole light out, made sure it was wired exactly the same, and the same issues occurs which is the running light remains dim.

    What would cause this? The remaining 4 cab roof lights are on full power. Recently had to replace the low voltage disconnect module on the truck which is a 2023 KW W900L.
     
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  3. FLHT

    FLHT Road Train Member

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    Check your ground wire..
     
  4. Mr Bob

    Mr Bob Light Load Member

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    my exact thought. lol
     
  5. OhNoTerry

    OhNoTerry Medium Load Member

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    I messed around with the plug itself and couldn’t get it to get back to being fully lit. It being a 2023, do you think it’s likely a connection issue with the plugs or possibly a ground wire gone back behind the panels in the cab?
     
  6. JB7

    JB7 Medium Load Member

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    First thing to do is get a voltmeter and check the voltage at the plug with the light disconnected. If you have 12v or more and the light is dim then there is a problem with the light itself. If you have less than 12v, something like 7 or 8, then the problem is elsewhere. If you can, take one of your original lights and plug it back in and see what happens.
     
    BoxCarKidd Thanks this.
  7. Mr Bob

    Mr Bob Light Load Member

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    Mar 17, 2015
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    try another light
     
  8. OhNoTerry

    OhNoTerry Medium Load Member

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    I put a brand new one on, same result.
     
  9. OhNoTerry

    OhNoTerry Medium Load Member

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    May 22, 2021
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    I’ll have to get a voltmeter. I slightly crimped the ground and powered female ends as the plugs were a tad bit loose, that didn’t do anything. I checked the ground wire that was connected at the back of the housing that *looked* good and clean. I’ll randomly hit a bump on the road and it’ll power up for a seconds and then go back to dim. Thinking once I clear the voltmeter aspect, I’ll have to put the housing and chase the wires.
     
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