Hey guys, I am having trouble with my trailer brakes. They are the standard electric controlled magnet brakes. I have a 94 f250 factory turbo truck with the factory brake controller plug and play hook up. All of my wires are reading proper voltage when they should....except for the brake wire. When I am not pushing the brakes I am getting 4.5 volts going to the trailer brakes....when I unplug the brake controller I get no voltage at the brake wire. What in the world could cause this? I am getting constant 12 volts on the black wire like I should. The problem with this is that the brakes lock up while I am driving. I need to use the trailer tomorrow. Do you all have any ideas? Thanks.
Trailer Brake problem, constant voltage on Brake wire
- Thread starter cardana24
- Start date
a little more information. I just check the wiring on the factory plug and play wiring for the brake controller. With the controller unhooked I only see 12 volts on the black wire like I should. As soon as I plug the brake controller in I get 4.5 volts on the blue wire....the same 4.5 volts I am seeing at the trailer brakes....how is this happening? I assume something has gone south between my brake controller and my 7 pin plug at the back of the truck.
Also I should mention that it's doing the same thing with two different brake controllers....one brand new and one that came with my trailer. Any help is appreciated.
Also I should mention that it's doing the same thing with two different brake controllers....one brand new and one that came with my trailer. Any help is appreciated.
boxathey
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is the brake controllers mounted as level as possible. i have found that to sharp of an angle can cause the controller to apply moderate braking.
did you check to make sure your brake switch is working properly. and that there is no voltage bleed on the switch wire. (the wire going to the controller not sure what color it is)
did you check to make sure your brake switch is working properly. and that there is no voltage bleed on the switch wire. (the wire going to the controller not sure what color it is)
Disconnect the red wire going to the brake switch, see what you get. If that don't do it, run another ground, white wire.
MIDNIGHT RIDER
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You may have already said and I missed it; but, are you running these voltage tests with the trailer plugged or un-plugged from the truck ??
When a magnet wears through, it is a dead short to GROUND, kills ALL the trailer brakes, and makes a controller act weird.
It is truly amazing when electric brakes actually work and work well for an entire trip; I am surprised they are D.O.T. legal.
When a magnet wears through, it is a dead short to GROUND, kills ALL the trailer brakes, and makes a controller act weird.
It is truly amazing when electric brakes actually work and work well for an entire trip; I am surprised they are D.O.T. legal.
Yeah they are pretty level....plus I don't think the older one matters since you just set the voltage, it does not vary unless I manually increase it. My newer controller does need to be mounted fairly level to work right.
Where is the brake signal coming from? i.e. where is the brake switch/
I'll try that in the morning.
Are you thinking there is a problem with the factory wiring?
You may have already said and I missed it; but, are you running these voltage tests with the trailer plugged or un-plugged from the truck ??
When a magnet wears through, it is a dead short to GROUND, kills ALL the trailer brakes, and makes a controller act weird.
It is truly amazing when electric brakes actually work and work well for an entire trip; I am surprised they are D.O.T. legal.
I am running the voltage test with the trailer un hooked...I also tested it at the trailer hooked and I tested it and the brakes and I am getting the same 4.5 volts back there. My brakes are brand new so I hope the magnets have not already warn though. They might have 100 miles on them.
MIDNIGHT RIDER
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That is true for the older non-electronic controllers.
However, on an electronic controller, there is some voltage at the BRAKE wire at all times; because, when no trailer is plugged in, the little GREEN light is not lit; as soon as the trailer is plugged in, the GREEN light comes on.
MIDNIGHT RIDER
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Take the controller out of the loop.
Controller dis-connected, trailer un-plugged, temporarily connect the controller's HOT wire to the BRAKE wire and test voltage at the plug.
If this shows a good 12-volts-plus, try the same test with trailer connected.
This will tell you if the problem lies within the controller or the wiring.
I finally got around to re grounding the ground wire in the factory wiring for the brake controller and it made no difference. I still get constant voltage at the trailer brake wire. When the brakes are not being pushed it shows ~4 volts at the rear of the truck, and when the brakes are being pushed it shows ~12 volts. This is all with the trailer not hooked up.
chevytaHOE5674
Full Access Member
When the brake pedal isn't being pushed do you have any voltage coming from the brake light switch to the controller?
Go to etrailer.com and dig around the instructions and get the wiring diagrams and look VERY CAREFULLY at the plug pinouts for the 7 pin connector and make completely sure that someone has not wired the connector backwards that goes to the brake s. SOmeone before me had done that on my truck and it gives you constant voltage going to your brakes because that becomes system ground and it is getting negative voltage constantly through the brakes and then when you hit the brakes it simply shorts voltage to ground on the trailer. I would get a roughly 4 .5v reading as well. I ended up rewiring everything.. The boneheads that installed the bed on that thing , if they had a brain, they would have taken it out and played with it. The truck has the tow kit and instead of using teh fuses and relays for the trailer or the brake controller plug in, they butchered teh harness and had ALL the lights running off the cab lights and brake controller hard wired in with gumby wiring running along teh frame. It all had to go.
chvycmnslvr68
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I dont know what type of controller you are using but some controllers have an inertia sensor in them to actualy apply the brakes and those units have a LEVEL SENSOR ADJUSTMENT SCREW on the side oppisite of the application adjustment control ... it usualy has to be turned with a nickel or dime the way the slot is designed .... otherwise if the brake controller just works on brake light input like my cheap one that applies the brakes to whatever I have them set to .. just bringing up the voltage slowly ... My type will test hot at the trailer plug all the time ... but when there is nothing hooked up I get an E1 code on my display and when I plug in the trailer it gives me the % reading that the brakes are set at ... if it is inirtia activated the LEVEL sensor setting is crutial and will apply the brakes all the time if not properly set ..or not come on at all if the oppisite direction ... but you should be getting either a red light or an error code when the trailer is unplugged ... if not your probably shorting into your taillights somehow or brakelights or turnsignal .. only a light will give the unit a false reading and make it think it has a trailer attached ... goodluck I hope this helps ...
I don't have anything to add I will however watch this thread closely for certain!...
I need to learn about this stuff a bit...
I need to learn about this stuff a bit...
