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Thread: Trailer brakes not working

  1. #1
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    Trailer brakes not working

    My trailer brakes stopped working on my dump truck. The green light on the controller is on, when the trailer is connected, but when you give the tabs a squeeze to test the brakes, the red light does not come on and the brakes have no effect. What could cause this? Could it be a bad ground on the trailer end of the electric brakes?? I have been chasing my tail with this...
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  3. #2
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    Re: Trailer brakes not working

    Quote Originally Posted by Keith Merrell View Post
    My trailer brakes stopped working on my dump truck. The green light on the controller is on, when the trailer is connected, but when you give the tabs a squeeze to test the brakes, the red light does not come on and the brakes have no effect. What could cause this? Could it be a bad ground on the trailer end of the electric brakes?? I have been chasing my tail with this...
    Start with ALL of the grounds!
    Mine will do something similar when it hasn't been used for a while.
    I fix it by rolling the gain control back and forth!
    I need to open it up and put some contact cleaner in there.

  4. #3
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    Re: Trailer brakes not working

    Some of the controlers have an minum angle they have to be at. If they get to close to vertical they won't work

  5. #4
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    Re: Trailer brakes not working

    Either the grounds, poor connections for the power wire, or worn magnets.

  6. #5
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    Re: Trailer brakes not working

    If possible connect trailer to another vehicle and test, and your truck to another trailer to test.


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    Re: Trailer brakes not working

    Do you have a breakaway switch on the trailer? is so pull it and see if the brakes work then... if not problem is on the trailer side... if breakaway works then problem is on the truck side probably the plug connection or maybe where the plug ties into the vehicle harness...

    More details on truck and trailer and controller: as I don't remember what you had for a dump truck

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  9. #7
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    Re: Trailer brakes not working

    sometimes you may get a lot of rust on the brakes/pads/magnets and won't make proper contact. wiring connection corrosion. broken wire.

  10. #8
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    Re: Trailer brakes not working

    So I checked all of the grounds and redid the connections. That didn't work unfortunately. I am going to have to check the magnets next I guess.
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  12. #9
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    Re: Trailer brakes not working

    Quote Originally Posted by Keith Merrell View Post
    So I checked all of the grounds and redid the connections. That didn't work unfortunately. I am going to have to check the magnets next I guess.
    One other thing to check... as I had this issue with one of our dump trailers a few years after we bought it new.... IF the manufacturer used the axle tube wires( the ones the run inside the tubes) eventually they wear though the wire insulation and WILL short out inside the axle tube!!! it will cause the brake controller to not work... and depending on the brand of controller it could give different indications... including no fault.

  13. #10
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    Re: Trailer brakes not working

    If your controller is the newer type like we have built into our 2015,2017,2019 ram trucks then the slightest wiring issue will disable the brakes

    Our new big PJ 25 foot gooseneck dump trailer had such a problem a couple months after we bought it brand new!!! it turns out PJ trailers runs the brake wires between the frame so if you go through a pothole and the one axle experiences a full drop condition it rips the wires apart this will cause the newer controllers to disable themselves even if the other 3 brake hubs are working perfectly!!! on a 2 axle trailer.

  14. #11
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    Re: Trailer brakes not working

    Thatís got to be frustrating with new equipment. This is a 2001 GMC 6500 and a Fleming trailer from the 80ís.


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  16. #12
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    Re: Trailer brakes not working

    Quote Originally Posted by Keith Merrell View Post
    That’s got to be frustrating with new equipment. This is a 2001 GMC 6500 and a Fleming trailer from the 80’s.


    Sent from my iPhone using Tapatalk
    so... do you have a breakaway switch on the trailer? up here they are required.. and if you get stopped they WILL pull the switch and tell you to drive forward... and it better have the brakes locked or you get red tagged!!!

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  18. #13
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    Re: Trailer brakes not working

    Yes, I have a breakaway.
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  19. #14
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    Re: Trailer brakes not working

    It could be that the wires to the brakes are broken possibly, I will pull the wheels tomorrow.
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    Re: Trailer brakes not working

    Just tested the plug on the truck side. Looking at a diagram, the pin at the 5 oclock position is the trailer brake pin. It has 12 volts constant! No pins are affected when I press the brake controller so it must be a problem on the truck side...
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  21. #16
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    Re: Trailer brakes not working

    Quote Originally Posted by Keith Merrell View Post
    Just tested the plug on the truck side. Looking at a diagram, the pin at the 5 oclock position is the trailer brake pin. It has 12 volts constant! No pins are affected when I press the brake controller so it must be a problem on the truck side...


    Depending on controller.... 12 volt constant with a DMM is different than 12 volt constant with a test light... you have to use an incandescent test light for enough of a load to make some controllers work correctly and test them.


    7pin flat(round) connector on truck at 5 o'clock sounds right for the brake lead...

    Did you pull the breakaway switch pin and see if the brakes get energized? you have to try to pull the trailer or have at least one wheel off the ground to try without pulling the trailer because when a battery energizes the magnets you most likely will not hear anything... it is only when you try to turn a wheel(by hand or pulling) you will find the wheels gets braked. if the breakaway pin works then the brakes are most likely good.

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  23. #17
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    Re: Trailer brakes not working

    Quote Originally Posted by ronsii View Post
    Depending on controller.... 12 volt constant with a DMM is different than 12 volt constant with a test light... you have to use an incandescent test light for enough of a load to make some controllers work correctly and test them.


    7pin flat(round) connector on truck at 5 o'clock sounds right for the brake lead...

    Did you pull the breakaway switch pin and see if the brakes get energized? you have to try to pull the trailer or have at least one wheel off the ground to try without pulling the trailer because when a battery energizes the magnets you most likely will not hear anything... it is only when you try to turn a wheel(by hand or pulling) you will find the wheels gets braked. if the breakaway pin works then the brakes are most likely good.
    Yep, that low amperage 12V is probably just for a circuit status check from the controller. Time to do some direct checks on the trailer circuits. I use a short pigtail with a receptical and a battery to check the trailer side. Usually when you energize the brakes you can hear a humming sound at the wheels.

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  25. #18
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    Re: Trailer brakes not working

    Quote Originally Posted by 12V71 View Post
    Yep, that low amperage 12V is probably just for a circuit status check from the controller. Time to do some direct checks on the trailer circuits. I use a short pigtail with a receptical and a battery to check the trailer side. Usually when you energize the brakes you can hear a humming sound at the wheels.
    Ok. In the morning I plan to run power from a battery to the brake pin on the trailer. I will also try the breakaway.
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  26. #19
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    Re: Trailer brakes not working

    Quote Originally Posted by ronsii View Post
    Depending on controller.... 12 volt constant with a DMM is different than 12 volt constant with a test light... you have to use an incandescent test light for enough of a load to make some controllers work correctly and test them.


    7pin flat(round) connector on truck at 5 o'clock sounds right for the brake lead...

    Did you pull the breakaway switch pin and see if the brakes get energized? you have to try to pull the trailer or have at least one wheel off the ground to try without pulling the trailer because when a battery energizes the magnets you most likely will not hear anything... it is only when you try to turn a wheel(by hand or pulling) you will find the wheels gets braked. if the breakaway pin works then the brakes are most likely good.
    Thanks. I have messed with air brakes before but not much with electric brakes.
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  27. #20
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    Re: Trailer brakes not working

    I should add that when we were having problems with the big dump trailer it would not work on any of the newer vehicles with the integrated controllers but worked fine on mine and a few other trucks that had aftermarket controllers... or at least I thought it was fine... just never noticed one of the wheels not braking because you could feel the brakes working when squeezing the manual brake lever on the controller... so I was convinced it was a problem in the pigtail on the trailer because it only affected the newer controllers.... and had given the underside wiring on the trailer a quick look.... maybe too quick because I hadn't noticed the one wire disconnected from one of the backing plates... anyways the newer controllers could 'sense' a wire was disconnected and it would disable the whole thing!!! so no brakes at all....

  28. #21
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    Re: Trailer brakes not working

    Look closely at your wiring. Almost all of the imported 7 flat (round) trailer connectors that were imported for many years had the wrong colors and purposes imprinted right on the connector. They had the 7 pin truck wiring diagram. Verify what you have and rewire as needed. You can use the same connectors just ignore the wire colors. The diagram that is on the trailer picture is the wrong one that propagated for so many years.




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  29. #22
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    Re: Trailer brakes not working

    SOLVED Bad controller. Thanks for the help guys. The brakes on the trailer were working when I tested them so I knew it was on the truck side.
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  31. #23
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    Re: Trailer brakes not working

    Quote Originally Posted by Keith Merrell View Post
    SOLVED Bad controller. Thanks for the help guys. The brakes on the trailer were working when I tested them so I knew it was on the truck side.
    Good to hear sometimes these electrical problems can just ruin your whole day... or night

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  33. #24
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    Re: Trailer brakes not working

    Quote Originally Posted by ronsii View Post
    Good to hear sometimes these electrical problems can just ruin your whole day... or night
    Lol yeah ghost hunting.
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