Trailer brake lights stuck on.

Discussion in 'Freightliner Forum' started by Diesel13230, Nov 30, 2023.

  1. Diesel13230

    Diesel13230 Bobtail Member

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    I have a 2019 122SD and the trailer lights are stuck on. I know that it is not the trailer. I’ve used multiple different trailers and I get power at the trailer plug with no trailer attached. The “Johnny arm” functions and when I engage it I hear the relay clicking. Does anyone know where I should go from here. What do I all need to check?
     
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  3. IH Truck Guy

    IH Truck Guy Road Train Member

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  4. Diesel13230

    Diesel13230 Bobtail Member

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    A pigtail where? At the trailer connector?
     
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  5. JB7

    JB7 Medium Load Member

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    upload_2023-11-30_19-4-3.png
    Tractor protection valve should be at the back of the cab, follow from the gladhands to the other end of the air lines.
    What about the tractor brake lights, they are ok?.
    Your problem is most likely the switch is stuck.
     
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  6. Diesel13230

    Diesel13230 Bobtail Member

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    yeah truck lights are operating fine. I found the valve but in your picture there is just 1 switch. Is there a second one for trailer or does truck and trailer run off same switch?
     
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  7. Diesel13230

    Diesel13230 Bobtail Member

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    Pretty sure this is the same valve you sent a picture of just has lots more stuff around it.
     

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    Rideandrepair Thanks this.
  8. JB7

    JB7 Medium Load Member

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    "follow from the gladhands to the other end of the air lines." They end up at the TPV which should be what is in your pic. The switch there is for the trailer brakes. You could even disconnect it and see if the trailer lights go out or test at the trailer plug. There is a thumbs up/Thank icon if the response was helpful.
     
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  9. Diesel13230

    Diesel13230 Bobtail Member

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    ok I will do this tomorrow and let you know what I find, thanks!
     
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  10. IH Truck Guy

    IH Truck Guy Road Train Member

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    Try a whole new 7way line.
    You might have a stray wire making contact with the brake lite circuit.
     
  11. Diesel13230

    Diesel13230 Bobtail Member

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    ok I could disconnect it at the trailer PD box and test continuity. Thanks for the advice I’ll see what I find tmrw.
     
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