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  1. #11
    Member
    Join Date
    Dec 2007
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    26
    Location
    Pacific Northwest (Washington)
    Tractor
    l3400

    Default Re: Electric Trailer Brakes Troubleshooting

    Soundguy I agree, and would check the resistance between the blue wire and ground because if there was a open then there wouldn't be any voltage drop causing 12 volts all the time.

  2. #12
    Elite Member
    Join Date
    May 2012
    Posts
    2,972
    Location
    Knoxville, TN
    Tractor
    Bobcat CT225

    Default Re: Electric Trailer Brakes Troubleshooting

    Quote Originally Posted by henryswe View Post
    Soundguy I agree, and would check the resistance between the blue wire and ground because if there was a open then there wouldn't be any voltage drop causing 12 volts all the time.
    ... but shouldn't there be zero volts on the blue wire when the brake pedal is not being pushed? Even if there is a dead short to ground, where would the +12v potential come from if the controller was not putting it onto the blue wire? I may be missing something here, in which case I apologize.

  3. #13
    Silver Member
    Join Date
    May 2001
    Posts
    151
    Location
    Tornado Alley
    Tractor
    L4350, L3430HSTC, L5740HSTC

    Default Re: Electric Trailer Brakes Troubleshooting

    If it wasn't so late, I have another truck I could hook it to and see if the brakes work with it. That said, I am sure I could just plug a 12v source to the blue wire on the trailer and see if the brakes locked. I now remember the other day, checking the voltage with the brakes attached and only saw 3-4 volts. I then checked continuity on the trailer wires and they were good.

    Lots to do in the morning.

  4. #14
    Elite Member
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    May 2012
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    2,972
    Location
    Knoxville, TN
    Tractor
    Bobcat CT225

    Default Re: Electric Trailer Brakes Troubleshooting

    Quote Originally Posted by JamesKubota View Post
    If it wasn't so late, I have another truck I could hook it to and see if the brakes work with it. That said, I am sure I could just plug a 12v source to the blue wire on the trailer and see if the brakes locked. I now remember the other day, checking the voltage with the brakes attached and only saw 3-4 volts. I then checked continuity on the trailer wires and they were good.
    You should see 10.5 volts or more measured at the lead of the magnet, when the controller's "activate" lever is fully pressed. The controller will put out 12v, but there is some loss in the lines; 10.5 is considered the minimum acceptable value. 3-4 volts is clearly low. As with any electrical problem, the first thing to do is to check the ground between the trailer and the truck. If you don't have a good ground, you will spend a lot of wasted time troubleshooting.

    If you measure 12 volts at the controller and 3-4 volts at the trailer, you're already onto something: something is soaking up that voltage between the controller and the trailer. I'd suggest measuring the voltage at the trailer connector on the truck. If it's also 12 volts, then the truck's wiring is probably okay, and you've likely got a problem in the trailer, or in the hookup between the truck and the trailer.

    You absolutely can activate the brakes by hooking the right pins on the harness to a 12 volt battery. Here's a good source for pinout diagrams:

    Trailer Wiring Diagrams | etrailer.com

    I have a 12 volt jump-starter battery pack that I used for testing. It was really nice to have a switch that could cut the battery on and off, instead of having to connect and disconnect an alligator clamp.

  5. #15
    Super Star Member Diamondpilot's Avatar
    Join Date
    Jan 2007
    Posts
    14,366
    Location
    Daleville, IN
    Tractor
    Jinma 254/284 Ford 861 Powermaster at work

    Default

    Quote Originally Posted by joshuabardwell View Post

    ... but shouldn't there be zero volts on the blue wire when the brake pedal is not being pushed? Even if there is a dead short to ground, where would the +12v potential come from if the controller was not putting it onto the blue wire? I may be missing something here, in which case I apologize.
    Many times the issue is corrosion on the back side of the trucks 7 pin plug. Check it thoroughly on both the front/plug side and the backside by dissembling it.

    Check the voltage at the trucks plug to eliminate.

    If you question the controller bench test it with a battery free from the truck.


    Chris

  6. #16
    Silver Member
    Join Date
    May 2001
    Posts
    151
    Location
    Tornado Alley
    Tractor
    L4350, L3430HSTC, L5740HSTC

    Default Re: Electric Trailer Brakes Troubleshooting

    Now that you bring the corrosion topic up, I see one thing I need to change. The trailer has one of those smaller round 6 pin connectors and I have an adapter that goes between it and the truck. I need to get one of the correct 7 pole ends and remove one failure point. I have checked and cleaned the adapter and get good connections through it but the trailer plug may not be getting a solid connection.

  7. #17
    Super Member crazyal's Avatar
    Join Date
    Dec 2003
    Posts
    5,888
    Location
    Northern Vermont

    Default Re: Electric Trailer Brakes Troubleshooting

    The way I test the magnets is by using a 12" adjustable wrench. When the magnet has 12v applied to it from the battery the magnet should be able to easily hold the weight of the wrench. With an inertia brake controller you'll either need to push the override lever or connect a 12v battery to the brake wire though. I suspect that 12 volts you are seeing right now is the circuit in the controller that tests to see if a trailer is connected. If you can easily measure the wire coming out of one of the magnets that connects to ground you can test for voltage there. You should see 0v. If you see much more than that then you're ground is bad.

    My guess is you have a ground issue. Unplug the connector from the back of the controller and use a section of wire to connect the wire going to the trailer brakes to the battery and try the wrench test. If it sticks then I would focus on the controller. I like testing this way because it puts the full amount of power into your trailer braking system and it tests your entire wiring system and grounds. Sometimes the ground is poor and only when you try to put the full amount of power through it will a flaw show up.
    Kubota L4240,Case 580K backhoe, Case 450 Dozer

  8. #18
    Veteran Member
    Join Date
    Sep 2002
    Posts
    2,367
    Location
    Michigan

    Default Re: Electric Trailer Brakes Troubleshooting

    It seems like 99% of trailer electrical problems are due to a poor ground. My advice is to not use the frame as a conductor. Wire is cheap, so just run a separate ground wire to each brake and light. I avoid crimp connections where water can get to them, opting for solder and shrink tape.

    In short, don't just fix the current problem, fix the future problems while you are at it.

  9. #19
    Elite Member
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    May 2012
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    Knoxville, TN
    Tractor
    Bobcat CT225

    Default

    Solder is actually a poor choice for connections where there is vibration. It has no give, so it cracks eventually. Wire nuts or crimp-on connectors are the recommended way of making automotive wire connections.

  10. #20
    Veteran Member
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    Sep 2002
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    Location
    Michigan

    Default Re: Electric Trailer Brakes Troubleshooting

    When using a soldered connection, you need to support the wire with a mechanical attachment so it doesn't flex at the solder joint (where there is a stress concentration). I disagree that crimping is superior in wet, especially wet and salty, applications like under a trailer. This is especially true because most people use the cheap $3 crimpers, not the good kind.

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