Trailer brake issue...

Discussion in 'Mechanic and Repair' started by TriCityLawnCareLLC, Mar 7, 2012.

  1. TriCityLawnCareLLC

    TriCityLawnCareLLC LawnSite Bronze Member
    from Ohio
    Messages: 1,025

    This will probably get moved to the mechanic section but thought i'd try to get some of you guys (who don't visit that section) to see this and maybe help me out.

    I bought a used trailer last year. tandem axle 3,500 each axle. It's a Big Tex trailer, year 2003. It came with electric brakes on the rear axle only. When i bought the trailer a year ago i also bought a Reese Pilot control box for the cab. I wired up the box correctly, even inserted the 40amp fuse in stud #1. im getting 10volts on the trailer brakes at the rear of my truck. But the box keeps telling me that there is no trailer hooked up, so my only guess is that there is not a closed circuit somewhere, correct? The box is putting out roughly 10volts when i squeeze the trigger, but it doesn't register any numbers on the display, only a little dot showing that it's hooked up.

    ive tested all plugs (truck and trailer) with ohm meter and they're good. ive gone all the way back to the brakes on the trailer. there' a black wire and a white wire (black:power white:ground) that run down the left-hand side (drivers side) of the trailer, once they reach the rear axle they get spliced with power going to the brakes on the drivers side then power and ground run from that splice across the trailer to the other brake.

    I cut the wires right where they were spliced, hit my brake pedal and tested, i'm getting 9.5volts of power. So i've deducted that I've got power to the brakes. OH, i forgot to mention, when i first started playing tinkering around today, i found out that something somewhere is crossed because the brakes were activated with no pedal or controller box. Then once i hit the brakes pedal the trailer brakes let up (freed up). So for a second it was reversed somehow, brakes applied = no trailer brakes and no brakes applies=trailer brake. But after i re-tested everything and hooked it all back up the problem went away. ???

    1. there are not power issues on the truck (2005 gmc sierra z71)
    2. Both trailer and truck plugs are fine
    3. Have good power and good ground all the way back to the trailer brake

    My Questions:
    1. Why does the reese pilot box show no trailer connected, even before i cut into the wires?
    2. How do i know if the electro magnet is good or bad?
    3. there are two wires that go into the magnent, they are both green, how do i tel which is positive and which is ground, or does it even matter?
    4. Was it a possible ground issue that cause my brake to be applied even though i wasn't applying the brakes?
    5. Where do i go from here to figure this problem out? Thanks guy.

    OH and from the rust on the inside of the brake hub, the brake shoes aren't engaging, only the magnent is. So tomorrow i'm going to pull the whole brake unit off and tear it apart and beat the rust off and lube it and get them function i hope. I hope someone reads this and can help out. Thanks.:usflag:
  2. TriCityLawnCareLLC

    TriCityLawnCareLLC LawnSite Bronze Member
    from Ohio
    Messages: 1,025

  3. tyler_mott85

    tyler_mott85 LawnSite Senior Member
    Messages: 582

    I've experienced and heard of problems with two different methods of wiring the plugs and when you go to wire in the brake controller when it comes to the truck to trailer connection that's where the wire gets crossed and you get brakes all the time. Specifically its only the two wires that control the brakes, obviously. This is the only thing I could think to explore with my limited knowledge of trailer brakes. I do not know anything about that specific controller so I cannot help there.

    I can also add a tidbit of info that trailer brakes do not self adjust like brakes on trucks/cars so you have to physically get a brake spoon and adjust the brakes as they wear down so even if you do not get any noticeable braking from the brakes they may be out of adjustment.

    good luck!
  4. Richard Martin

    Richard Martin LawnSite Fanatic
    Messages: 14,699

    I agree. It sounds like the truck and trailer are not wired the same.

    You can test the function of the trailer brakes with a 12 volt battery. Just jack the trailer up and apply 12 v to the blue wire. The brakes should keep the wheel from turning. Even if there is a problem with the brakes you should hear the magnet humming. The magnet wiring is not color coded. Either side to ground with the other connecting to blue.

    I do a lot of trailer wiring repairs and this is how I wire all of the 6 and 7 pins up.

    trailer wiring 6 pin.jpg

    trailer wiring 7 pin.jpg
  5. TriCityLawnCareLLC

    TriCityLawnCareLLC LawnSite Bronze Member
    from Ohio
    Messages: 1,025


    I'm glad you've got experience in this!! After posting, i went out and fiddled around some more and was able to get 12v on the black wire (on the trailer) at the actual drum where before i only got 9.5, now obviously the black wire wasn't hooked up to the brakes, i cut the wire to test.

    Bare with me as i try to figure this out. So on my trailer i have a blue wire that comes from the trailer plug (6 hole trailer plug which i plug into and adapter with 6 holes that plugs into my truck which has 7 point) and goes into the break-away box but i have no blue wire that runs all the way back to the trailer brakes, only black and white wires. My understanding is that the black should provide power to the magnet while the white acts as a ground.

    Now regarding the break away box, something is also amiss because i'm not getting any volts whatsoever at the battery. The battery is also dead, but i was under the impression that the battery was for the break-away only.

    also,Should the control box in the cab be putting out 12v? I left it hooked up but i unplugged the blue wire and then squeezed the trigger and I was only getting like 6-7 volts.

    So, i thought maybe i had it figured out, but now i feel like i'm back at square one.
    The magnet was working enough earlier to slow the wheel down to where i was barely able to turn it, but the actual shoes didn't even move, i need to free them up. I really appreciate the help and hopefully we can figure this out. I'm still perplexed as to why the control box isn't working? So many questions
  6. dhardin53

    dhardin53 LawnSite Senior Member
    Messages: 710

    You need of a new breakaway battery. The low or no battert is giving you the bad hook up signal.
    Last edited: Mar 7, 2012
  7. TriCityLawnCareLLC

    TriCityLawnCareLLC LawnSite Bronze Member
    from Ohio
    Messages: 1,025

    I also failed to mention that i only get 12v back on the black wire at the trailer brakes when i hit the pedal. The controller box, when applied does nothing
  8. dhardin53

    dhardin53 LawnSite Senior Member
    Messages: 710

    If you replace the battery all will work fine, The breakaway battery is only in effect if and when the connection to the truck and or control box is broken.

    The hand brake on the control box will not let you lock the trailer brakes for safety reason. The pedal will give off 10 to 12v for maximum braking power.
  9. dhardin53

    dhardin53 LawnSite Senior Member
    Messages: 710

    Some years ago when I was traveling with our band. The bass player was driving the truck pulling the equipment trailer. He had the truck on cruse control and trying to get comfortable he rested is knee agents the control box brake. So the trailer was trying to stop (7v) and the truck drooped out of over drive and went to racing to keep the speed stable. Scared the bajesues out all of us. But there was nothing wrong after he hit the brake pedal.
  10. Richard Martin

    Richard Martin LawnSite Fanatic
    Messages: 14,699

    Okay. We're going to fix your wiring one problem at a time. You have so much buggered up that it's near impossible to tell what's going on.

    The place to start is at the truck plug. Believe it or not, not all 7 way plugs are wired the same, even when they come from the factory.

    Then we're going to jump to the trailer and identify which wire does which function.

    Then we're going to put a new 7 pin plug (dirt cheap) on the trailer. A lot of problems start when using adapters. I have no idea how the adapter is wired. There are no universal rules or laws governing the wiring so everybody does pretty much what they want to.

    Once we have the truck and trailer wired the same then we can work on getting everything working on the trailer.

    This is the exact way I would fix your trailer if it was sitting in my driveway.

    Like I said, start at the truck. Print out the 7 pin diagram I posted above. When you're looking at the diagrams you're look at the pin side. The wires would go in the back of the diagram if it were a plug.

    One by one test the pins on the truck. You may need a helper to activate the truck brakes so you can be sure that brake power is going to pin number 2 as shown in the diagram. Test all 6 pins that go around the outside and make sure they do what the diagram says. The center 7 pin may have 12v constant, may work with the backup lights or it may not have anything. That is an optional pin and you can do with it as you like.

    If the pins don't do what the diagram says, make a note of it on the diagram that you printed out. We will have to make sure the trailer end is wired the same way. That or you can dig into the wiring on the truck and correct it. Since you've never done this before I think it's far easier just to wire the trailer to match the truck. Chances are good though that the truck is wired correctly.

    I'll be in and out all day so I'll check on your progress here at Lawnsite. Once you complete a section we'll move to the next section.

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