Electric Trailer Brakes Troubleshooting

[HappyOne]

Today I was trying to figure why my trailer brakes are not working. When I activate the brake controller, I get a sound like the magnet is being energized at each wheel but no braking. I took the brakes apart and everything looks good and moves like it should. I repacked the bearings and put it back together. I started working my way forward, and noticed there is a constant 12 volts on the trailer brake pin when disconnected. I checked the back of my trailer brake controller and it too shows 12V full time. Is having voltage constantly on the blue wire is normal. This is even with the key off.

 

[Willl]

Did your 'break-away' switch get accidentally pulled ?

 

[joshuabardwell]

The blue wire is the brake wire. Voltage on that wire causes the brakes to activate.

If your emergency brake pin got pulled, you would have voltage on the blue wire even with the truck disconnected, but it wouldn't last long because the battery would die in 10 or 15 minutes.

You can use a compass to check that the magnets are active. It will deflect strongly when placed near the hub. Alternatively, use an ammeter to measure the current draw when the brakes are active. Each brake should draw something like 2 amps... I'd have to pull out my owner's manual to give you a more accurate number.

I'd the magnets are activating but the wheels aren't stopping, you have a mechanical defect, but it could be as simple as having to adjust the shoes.

 

[joshuabardwell]

... just thinking about this some more. Let's assume that the issue is not your emergency break-away system activating the brakes, and you really do have voltage coming out of the back of the controller all the time. How could this happen? One way could be that the controller is defective. Another way could be that your 12v accessory line in the trailer harness (red or black wire--only present on 6- and 7-pin connectors) somehow got shorted to the brake (blue) wire. Either way, the effect would be that the brakes would pull all the time. If the pull was insufficient to lock up the wheels, then the brakes would drag until the shoes wore away, and you would be in exactly the situation you are in now: brake magnets activating, but no actual braking force.

Either way, the next step is to figure out where the 12 volts on the blue wire is coming from. 12 volts on the blue wire equates to full-on braking.

 

[joshuabardwell]

Here's a chart showing the amps draw for the size and number of brake magnets that you have. This can be tested with an ammeter as discussed above. You will need to disconnect one brake and put the ammeter in-line to measure the amps.



Be careful not to exceed your ammeter's rating. Many home-use multimeters support up to 10 amps DC. That would be exceeded with four 10.25" brakes, for example. You can test individual brakes by disconnecting them and then connecting them one at a time.

 

[skipmarcy]

My Tekonsha Voyager controller instructions say that when the vehicle/trailer is static (not moving) and the brakes are engaged there will be slight magnet activity but not enough for braking action. The controller senses deceleration and if I'm not mistaken increases amperage to the blue brake wire, not increased voltage. I believe you should read 12v but very little amperage while checking the brakes while not moving. I don't know this for a fact, just assuming, plus your controller could be totally different. I would make sure you have a very solid ground between your trailer and tow vehicle - I see just as many problems from lack of a good ground on trailers as anything else. You can't rely on just the ground between the hitch and ball mount and trailer for lights and/or brake operation.

 

[joshuabardwell]

My Tekonsha Voyager controller instructions say that when the vehicle/trailer is static (not moving) and the brakes are engaged there will be slight magnet activity but not enough for braking action. The controller senses deceleration and if I'm not mistaken increases amperage to the blue brake wire, not increased voltage.

Of course. I forgot all about inertial controllers. I assume that you're activating the brakes by pushing the "activate" lever/button on the controller vs. the brake pedal. The "activate" lever/button should always (in every case I've seen) activate the brakes even if the truck is not moving.

In every case that I've seen (which, granted, is not a lot, but it's some), the controller activates the brakes by increasing voltage from 0 to 12. I think that's how they all work.

 

[sam5570]

i might be on the wrong tract but how is your controller wired ? where is the hot wire connected?

 

[HappyOne]

Wow, lots of good ideas. This trailer does not have a brakeaway system. The controller is a Tekonsha Voyager XP and it's on a 2008 Tundra. I will have to go out in the morning and check some of the things you guys suggest.

 

[Soundguy]

if I'm not mistaken increases amperage to the blue brake wire, not increased voltage. I believe you should read 12v but very little amperage while checking the brakes while not moving. .

wow.. i see someone who skipped out on electronics 101

series current is a function of supply voltage and load resistance .

i can tell you the laod resistance ( magnets ) isn't changing...

thus to vary curret.. you vary system voltage.

E=IR

soundguy

 

[henryswe]

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.

 

[joshuabardwell]

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.

 

[HappyOne]

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.

 

[joshuabardwell]

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.

 

[Diamondpilot]

... 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

 

[HappyOne]

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.

 

[crazyal]

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.

 

[Travelover]

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.

 

[joshuabardwell]

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.

 

[Travelover]

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.