Trailer brake problems..

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hacksaw1340

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Sep 11, 2010
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So I am still confused about trailer brakes.  I've read about all I can read and have a decent understanding but I still don't "get it" ..   

My buddy has a used trailer he picked up and the controller in my truck or his, is showing no trailer.


With no truck connected and stand alone trailer and good battery voltage
Checking the brakes.  I put my volt meter on ohms and read from the blue wire (pin 2 of the connector) to ground (Pin 1 of the connector) 1.6 ohms.    Is the blue wire supposed to show open?

Testing Brake Magnet Resistance

Further testing can be done with an ohmmeter, using the ohmmeter function on the multimeter check the resistance between the brake magnet wires. If the resistance is not within the specified range (see specifications below) then the magnet will need to be replaced.

Well..  I dont know how they are wired,  parallel-series or what.    Just thinking, I should see more than 4 ohms, and possible up to 16.

Brake Magnet Resistance Specifications
10 and 12 Inch Brake Magnets 7 Inch Brake Magnets
3.0-3.8 Ohms 3.8-4.0 Ohms

Well.. now I am really lost.. I measured my trailer and received the same ohm reading.  about 1.6
 

Mopar1973Man

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Jul 4, 2011
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New Meadows, Idaho
Is the blue wire supposed to show open?
No. Your seeing the combined resistance of all 4 brake magnets.

All brake magnets should be wired in parallel. So you would have to crawl under and separate each magnet and measure the ohm of each one separately to see the independent ohm number. But if you just probing the wires near your still going to see combined ohm value till you separate each one.
 

hacksaw1340

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Tulsa
Is looking at the combined resistance not a good idea?    In other words,  wont really way anything in the way of electrically OK?

Just curious how the brake controller knows ' it's all good".  Kind has me baffled.

Thanks for the info!
 

Mopar1973Man

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No. Sorry to say because you could have mixed bag of resistances and still be close to right.

But if you separate all the magnets and check you see if there is are open or shorted. Now you'll see if there is any truly damaged magnets in the system. Remember the brake controller is looking for major failure like open circuit (disconnected) or shorted (failed magnet). You got to remember these brake controllers work with single, double, or triple axle trailers so ohm value will be all over the map.
 

rvpuller

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Feb 12, 2010
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380
I just went through a nightmare with a short in the trailer brakes that was not there all the time, it ended up being the wiring going through the front axle but I got some very good lessens on trouble shooting electric brakes. First measuring the resistance at the plug does not tell yo much because it's so low because the magnets are in parallel. The first thing to do is separate the brake wires (blue and White) where the plug cord connects to the trailer, that also means isolating the white wire from the ground on the trailer,you want to make sure there is a continuous circuit all the way to the magnets because you can not rely on the trailer ground to run the brakes. Then cut the wires connecting the back axle and check the resistance of the at the isolated wires and it should be around 1.9 ohms, then check the back axle where you cut it lose and it should be close to the same. With that low of resistance you have  to make sure you have a good meter connection. If you have the front or back read around 3.8 then you have a bad magnet on that axle. It's matter of isolating the axles and then the individual magnets to find the problems. I ended up rewiring both axles to solve the short I had, I used regular butt splices to reconnect the magnets and sealed them with silicon to make them water tight, my wires also run on top of the axles instead of inside so hopefully no more shorts. The guy that wanted our spot in the NFS CG wasn't to happy because we had to stay one more night to get the problem fixed.

Denny     
 

hacksaw1340

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Joined
Sep 11, 2010
Posts
41
Location
Tulsa
Hi Denny,

Thanks for relaying your experience.  sounds like a great approach.  I purchased some butt connectors and some stuff a friend recommended called liquid tape.  It's like black electrical tape in goo form. 

I think we are set for starting this project Tomorrow or Tuesday.  I will let you know all know how we did. 

Thanks again,

Rik
 
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