Blowing trailer fuse clearance/tail lights

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by Stonegirl, Jun 27, 2022.

  1. Stonegirl

    Stonegirl Bobtail Member

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    Jun 14, 2021
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    I have a 2017 peterbilt 389 day cab. Does anyone have a wiring diagram for under the hood fuse box to trailer lights. I cant figure it out ive hauled multiple trailers and same problem on 4 different trailers it varies on how long it takes for problem to happen. But as it sits right now i put a new 30 amp fuse in turn on lights instantly cooks the fuse and when i say it cooks the fuse it has melted it under my finger without popping the fuse! Also i can hear it click as soon as i turn on lights. All my truck lights work and it only is affecting my marker/clearance/tail lights. Ive tried unplugging the trailer lights from both the trailer side and the truck side of plug in the back. Im not sure if there is something that tells the power to flow to the trailer and not when its unplugged. Because it doesnt happen when i unplug from trailer either way (from truck or trailer side). You would think if it was my trailer plug it would do it still if it was unplugged from trailer or not....right but its obvious its a problem not associated with trailers im lost help please!
     
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  3. D.Tibbitt

    D.Tibbitt Road Train Member

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    Check all wiring on truck to make sure it not shorting on the frame somewhere. That's usually what it is when lights are blowing a fuse.
     
  4. The Crossword Trucker

    The Crossword Trucker Heavy Load Member

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    Feb 21, 2015
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    Have you ever damaged your 7 wire pigtail or the plug for it on the truck by forgetting to disconnect it and driving off?
     
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  5. Stonegirl

    Stonegirl Bobtail Member

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    Jun 14, 2021
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    No sir brand new plug aswell
     
  6. Stonegirl

    Stonegirl Bobtail Member

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    Jun 14, 2021
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    So i found a short finder tool it willbe here tomorrow
     
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  7. D.Tibbitt

    D.Tibbitt Road Train Member

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    Apr 26, 2013
    Gettin' down westbound
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    You may be able to find it by getting underneath the truck and checking all that wiring tucked against the frame. Look for any exposed wire and check to make sure it not touching anything else
     
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