Trailer lights

Discussion in 'Shop Talk' started by scottdoyle, Jan 10, 2005.

  1. scottdoyle

    scottdoyle Active Member

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    I just hset up a pair of lights on an open faced trailer. Everything is working as it should except for when I turn on the headlights. They will stay on with the lights on but when I hit the brakes they go out. Any Ideas?
     
  2. moopups

    moopups In Remembrance

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    Sounds like a ground issue. The standard wire color used for 4 wire trailer light is as follows;
    Yellow is left turn signal/stop light.
    Green is right turn signal/stop light.
    Brown is running/parking lights.
    White is ground.
    The signal/stop wires connects to the red trailer light's wire.
    Thge running/parking wires connect to the black trailer lights wire.

    The next thing to look for is; does your vehicle have amber turn signals, and red stop lights? If yes then you need to accquire an adapter plug in to be wired into your vehicles system. If your turn signal/stop lights are both red, then the standard 4 wires unit will work. Any Rv or speciality plug in does not use the same color scheme.
     

  3. rambler

    rambler Well-Known Member Supporter

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    I'm not following which lights go out, the headlights, brake lights, or running lights.....

    But, 75% of the time when there is an odd lighting problem on a trailer, it is a ground issue.

    --->Paul
     
  4. scottdoyle

    scottdoyle Active Member

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    the lights completely go out on the trailer when the headlights are on and I press the brake. The lights on the vehicle stay the same.
     
  5. moopups

    moopups In Remembrance

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    In that the brake light system goes to direct ground when the vehicle brake lights are activated, this would indicate that the trailer lights are recieving their energy from that circuit rather than from the lights only circuit.
     
  6. John Hill

    John Hill Grand Master

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    Yes, I too think it is probably a grounding issue and I suspect the light fittings on the trailer are not grounded? When you turn the lights on the current flows through the trailer lamps but instead of returning via the earth it flows through the vehicle brake lights to ground. Applying the brake raises the voltage on the vehicle brake lamps which no longer present an easy path to ground.


    If the light fittings are attached to wood or fibreglass etc they need a separate ground wire.

    What happens when you apply the brakes with all lights off?
     
  7. scottdoyle

    scottdoyle Active Member

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    when I apply the brakes with all lights off it works properly.
     
  8. james dilley

    james dilley Well-Known Member Supporter

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    first you need 2 ck your connections and hopefully you spliced into the wiring harness of the tow unit and have a good ground second the pigtail can and will short out if not protected by a connecter or a good grade of tape try checking the lights wire by wire and make sure there are no bare wires
     
  9. Rosarybeads

    Rosarybeads Well-Known Member

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    Sounds like our truck & trailer, only we know what caused ours: our geese got under the truck and started nibbling. :D :D
     
  10. John Hill

    John Hill Grand Master

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    OK, I think we are making progress on this one.

    Assuming the light units on the trailer are not adequately grounded the current for the brake flows through the brake lights then instead of going directly to ground it splits and flows through the other lights of the trailer and the truck. This split current is not enough to light those lamps to appearances are that everything is OK. Thats what I think might be happening.

    Being so rash as to venture an opinion from so far away I too suspect it is a grounding problem in the trailer, more specifically I think the light fittings are not grounded to the trailer body or if they are plastic fittings the internal ground is not connecting to the trailer body.
     
  11. scottdoyle

    scottdoyle Active Member

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    Thanks for everyones help. Guess I will look for a grounding problem.