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Trailer marker lights fuse keeps blowing

Discussion in 'Trucks [ Eighteen Wheelers ]' started by #beardedmechanic, Jul 16, 2019.

  1. Jul 16, 2019 #1
    #beardedmechanic

    #beardedmechanic Bobtail Member

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    Jul 16, 2019
    0
    2014 T800 kenworth- trailer marker lights work fine the fuses OK until I start the truck then the 30amp-fuse blows I disconnected the trailer Put new fuses and and all work fine as power to pins good..untill i start the truck then the fuse blows...I also noticed the trailer marker relay to be running warm to hot.. i checked where the pins are connected to on the tractor side and cannot find any open wires the truck faily new... Trying to avoid bringing to shop
     
    #beardedmechanic, Jul 16, 2019
    #beardedmechanic, Jul 16, 2019
    #1
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  3. Jul 16, 2019 #2
    Old Man

    Old Man Road Train Member

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    Apr 3, 2009
    Oklahoma City, OK
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    Is it when you start the truck or when you first turn the key. Turning the key powers up the center pin for the abs, remove fuse or breaker for the abs and test again.
     
    Old Man, Jul 16, 2019
    Old Man, Jul 16, 2019
    #2
    FlaSwampRat Thanks this.
  4. Jul 16, 2019 #3
    AModelCat

    AModelCat Road Train Member

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    Canuckistan
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    Well you're 10 steps ahead of most by isolating the trailer. We know the issue is 100% the truck. What I would say is likely is the harness has chaffed thru on the frame or a bracket BUT is only making contact once the engine cranks over. The torque of the engine is likely causing the chassis to flex and its causing the chaffed wire to ground out. With the engine off, there's no flexing so the wire doesn't touch the frame. Sounds unlikely but I've seen it happen once or twice. I'd start at the trailer plug and work your way back.
     
    AModelCat, Jul 16, 2019
    AModelCat, Jul 16, 2019
    #3
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