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