Shorting electric brakes - Fiberglass RV


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Old 07-04-2018, 10:10 AM   #1
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Shorting electric brakes

My brake controller is showing my camper brakes have a short. I have Dexter 7" brakes. Any suggestions on where to look first?

Thanks
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Old 07-04-2018, 10:55 AM   #2
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Short

Shorted with the trailer plug in or out?
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Old 07-04-2018, 11:12 AM   #3
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Short

Behind each wheel is the backing plate that holds the brake assembly. Two wires come out of that plate. Look right where they disappear through the plate. Have they been stretched or pulled on by an exterior force like road debris? Then about ten inches or so towards the hitch that brake pigtail connects to the wiring harness of the trailer. Check those connectors. They may be covered by a split plastic protector tubing. As Frank said, next place is all around the places where the trailer plugs into the tow vehicle. Finally, if no joy on the exterior checks, pull the wheel and drum and check the wire at the oval brake magnet. (Those are the wires that disappeared into the backing plate)
Pretty much has to be one of those places.
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Old 07-04-2018, 11:29 AM   #4
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Agree with the 2 previous posts, also the brake positive wire from the brake controller, through the tow vehicle, hitch plugs, trailer, to the trailer brakes is blue. Brake return/negative/common wires are white. The other factoid is that the brake wires have no polarity, so doesn't matter whether the brake positive (blue) wire is connected to one brake wire or the other.
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Old 07-04-2018, 11:30 AM   #5
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Shorted with the trailer plug in or out?
Short is when trailer is in tow. No shore power connected.
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Old 07-04-2018, 12:11 PM   #6
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I recently isolated the 12v ground wires from the frame. The brakes continue to be grounded to the camper frame. Could that be the missing link?
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Old 07-04-2018, 12:22 PM   #7
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Isolating the 12v common wiring from the frame is fine but the brake return/common/negative/white wires must be attached to the return/common/negative/white wire that you see in the trailer side hitch plug, which can be traced back to the tow vehicle frame or tow vehicle battery negative. The common/negative wire on the tow vehicle side hitch plug may be a different color. Doesn't matter.
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Old 07-04-2018, 12:24 PM   #8
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So yes, you may have introduced the problem. Sometimes one of the two wires hanging from the brake is simply attached to the frame.
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Old 07-04-2018, 01:18 PM   #9
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Is there a designated ground and a designated power with the Dexter brakes? Does it matter how it is wired?

I wired in the brakes years ago. Worked fine till recently.

I looked at the wires and can't visually find a short. It seems that the ground wire to the brakes is a point that the system is still attached to the frame. Missed that one! So the brakes are attacked to the negative and the frame.

I'll disconnect wire to frame and run directly to brake. I don't think that should change anything, but who knows.

Maybe my only other choice is to pull apart the brakes. I hope not.
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Old 07-04-2018, 01:34 PM   #10
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the brakes aren't connected to anything other than the 7-blade pigtail, and the breakaway safety switch (which connects them to the battery if its pulled).

the brakes don't care about polarity, they are an electromagnet.

why did you isolate your trailer frame from ground?
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Old 07-04-2018, 01:46 PM   #11
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The electromagnet can become worn and eventually the coil will short to the drum when applied. That in turn will short to the spindle and frame through the bearings. This will be intermittent and the brake behavior will be erratic. I had tat problem and it was a pain to diagnose. I ended up buying new brake assemblies (with self adjustment - well worth it).
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Old 07-04-2018, 02:12 PM   #12
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Mark, even though its common practice to simply attach one of the brake wires to the frame, this is not the most reliable method. In either case (whether using the trailer frame for common, or instead using wires), all brake circuits need to run from the brakes through the 7 blade plug to the tow vehicle. So make sure you have continuity back to the 7 blade plug.
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Old 07-04-2018, 02:14 PM   #13
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On our last trip through the U.S. our brakes shorted out inside the 7pin connector. When I took the connector apart only 2 of the 7 wires were still secure. The other 5 wires fell right out of their holders.
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Old 07-04-2018, 09:51 PM   #14
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Originally Posted by John in Santa Cruz View Post
the brakes aren't connected to anything other than the 7-blade pigtail, and the breakaway safety switch (which connects them to the battery if its pulled).

the brakes don't care about polarity, they are an electromagnet.

why did you isolate your trailer frame from ground?
I isolated 12v- from the frame because I have an onboard battery and wanted to limit frame corrosion.

I will try to complete the isolation with the brakes as I have one negative wire under the camper to use.

Thank you for confirming that the electro magnets in the breaks don't require the wires to be hooked up in any order.

It's raining a bunch here and under the camper is muddy. As soon as I head home I'll play with the wires and tell you all if the 12v- wire grounding to the camper was the issue.

I hope it is.

Thanks.
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Old 07-04-2018, 09:51 PM   #15
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Originally Posted by John in Santa Cruz View Post
the brakes aren't connected to anything other than the 7-blade pigtail, and the breakaway safety switch (which connects them to the battery if its pulled).

the brakes don't care about polarity, they are an electromagnet.

why did you isolate your trailer frame from ground?
Thanks John
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Old 07-04-2018, 09:58 PM   #16
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The electromagnet can become worn and eventually the coil will short to the drum when applied. That in turn will short to the spindle and frame through the bearings. This will be intermittent and the brake behavior will be erratic. I had tat problem and it was a pain to diagnose. I ended up buying new brake assemblies (with self adjustment - well worth it).
Was it the power or 12v- that shorted to the frame?
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Old 07-05-2018, 12:08 AM   #17
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Was it the power or 12v- that shorted to the frame?
FYI Markz. The brakes get their power from the tow vehicle, which is a 12 volt DC system.
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Old 07-05-2018, 08:10 AM   #18
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Was it the power or 12v- that shorted to the frame?
That is an interesting question, I was wondering the same. The only way to find out would have been some sort of careful resistance measurement from the coil leads to the point where the coil wires were exposed. After the electromagnet was out, I did not know which lead was +12 and which was ground. So I can only guess from the behavior and believe that it was shorting close to the +12V side and the brake became ineffective.
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Old 07-05-2018, 09:55 AM   #19
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My 1986 Scamp 13 has one lead to each brake coil grounded to the frame from the factory. They have to be cleaned and re-attached due to exposure. Scamp saved about 12 feet of wire by attaching to the frame instead of the negative of the battery.
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Old 07-05-2018, 07:40 PM   #20
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Mark, even though its common practice to simply attach one of the brake wires to the frame, this is not the most reliable method. In either case (whether using the trailer frame for common, or instead using wires), all brake circuits need to run from the brakes through the 7 blade plug to the tow vehicle. So make sure you have continuity back to the 7 blade plug.
Everything I checked so far looks good. Before we left, I disconnected the last point known to connect with the frame. Still have the short. Ugh.
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