Brake Lights help

Discussion in 'Trucks [ Eighteen Wheelers ]' started by OW/OP Wolfman, Apr 20, 2015.

  1. OW/OP Wolfman

    OW/OP Wolfman Light Load Member

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    Feb 1, 2014
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    Last night I connected to the trailer and found this problem:

    1. The brake lights on the truck and trailer work if the running lights and headlights are turned off.

    2. If the headlights and running lights are turned on then there is no brake lights on the truck and the trailer brake lights are fully on.... Even though the brake pedal is not pushed.

    3. If the headlights are turned on the running lights on the brakes are not working.

    4. The brake lights flash if hazard lights are turned on.

    5. If I activate the turn signal to the left or right both the brake lights flash as if they are hazard lights instead of giving a left turn signal or right turn signal.

    6. The trailer ABS yellow light, lights up and goes off sometimes.

    Any ideas?
     
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  3. GrapeApe

    GrapeApe Road Train Member

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    Probably corrosion in a a connector somewhere crossing wires. Does it work normally when you disconnect the trailer?
     
  4. OW/OP Wolfman

    OW/OP Wolfman Light Load Member

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    Feb 1, 2014
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    Nope, not now.

    With the trailer disconnected the tail lights don't function when I turn on the headlights.

    With the the headlights turned off, if I push the brake pedal the tractor brake lights flash on.

    I think something on the tractor is wrong. Something corroded, crossing and touching, or just plain wore out. Maybe a light switch or turn signal. Whatever it is its throwing off the trailer lights I think.
     
  5. xsetra

    xsetra Road Train Member

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    To check your trailer independent from your tractor. Get a battery and hook into each line with a jumper wire. Make sure you have the ground to battery.

    I just had a light problem this weekend also. I changed the old corroded trailer female connector. When I turned 4-ways, brakes, and running lights all on. All the lights would flash. If I turned each one on individually everything worked ok. I found the ABS wire was feeding back from the trailer as a hot feed. With power coming from tractor and feedback from trailer the circuit breakers were popping. So I disconnected trailer wire ABS at breaker and everything is fine.


    Have to chase down the short tonight.
    Check your grounds. You could have a short in any of your lights also.
    Good luck.
     
  6. RSQ20

    RSQ20 Medium Load Member

    You are reporting issues with the trailer disconnected...

    Dont bother with the trailer until the tractor is working OK, check for a stuck relay or a circuit short to ground...

    ... Philip
     
  7. GrapeApe

    GrapeApe Road Train Member

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    Start isolating the problem. With your key on and no lights on, you should have good power to the center pin. Check for any voltage at any other pin. Basically turn on each thing in the pig tail one at a time and look for voltage crossing to a pin that should be off.

    That's about all I can tell you, not knowing the year, make, model of the truck is an huge limitation in helping you diagnose.
     
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