Testing Electric Brake at Tow 7 Pin Connector - Fiberglass RV
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Old 11-05-2019, 03:22 PM   #1
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Name: Huck
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Virginia
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Testing Electric Brake at Tow 7 Pin Connector

I'm having a problem with my electric brakes and thought it made sense to make sure there was voltage on the electric brake pin on the tow before looking at the trailer brakes.

I did it by myself so thought it might be helpful to anyone else who didn't have a helper.
  1. Use your voltmeter (on dc) and see what the voltage is between the ground pin and brake controller pin. This is the voltage when the brakes aren't applied. I got about 2v.
  2. Set the brake controller to the highest setting (14 on mine).
  3. The manual override on the brake controller needs to be all the way to the left. I used duct tape to hold it. When you go to the back of your tow, the brake lights should be on.
  4. Repeat step 1. With the brake on, I got a little over 12v.
  5. Remove the tape and return brake controller to prior setting.
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Old 11-05-2019, 06:30 PM   #2
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I normally just turn on my four way flashers to check.
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Old 11-05-2019, 07:47 PM   #3
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Originally Posted by Daniel A. View Post
I normally just turn on my four way flashers to check.
4-way flashers should not power the brakes!

So I assume you mean you use the 4-way flasher to check the lights, or to check that the umbilical cord is connected. I do the same, and its a good practice, but it does not test the connection to the trailer's brakes.

Checking for voltage on the brake line to the trailer when the controller override in used is a good check. I think the only thing it might miss is if the brake pedal activation is somehow malfunctioning.

So it would be good to also check the brake line voltage when the brake pedal is activated. But with a proportional controller (which is the type you probably should have), the brake voltage (and current) depends on whether or not you are decelerating*. So you would want to know the voltage when you are towing AND slowing down WITH the brake pedal pressed. Needless to say, this is hard to check with a temporary connection using a multi-meter. But a very good brake controller will show the voltage and also the current so you can tell how much power is going to the brakes under all these scenarios. The Tekonsha P3 Electronic Brake Control is one that does this.

* The P3 will “HOLD” your trailer with 25% of power setting while you are at a standstill with brake pedal applied for longer than 5 seconds, so this is a method for checking the break pedal connection while not moving.
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Old 11-05-2019, 07:48 PM   #4
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Originally Posted by Huck View Post
I'm having a problem with my electric brakes ...
Whats the issue you are having?
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Old 11-05-2019, 09:36 PM   #5
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Trailer brake test

Another check is to measure brake current with a fully charged RV battery. It’s best to check while all is OK and then you will have a reference. Here is my note, but remember, the leads are the weak point on a HF meter, so they will get warm if left connected. The brakes may still need adjusting of the star wheel, electrical is only part of it.
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BRAKE I.jpg  
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Old 11-06-2019, 05:47 AM   #6
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Whats the issue you are having?
They don't work.

I know they worked with my old tow, but I bought a van to replace it and I'm not sure if the brakes have worked since then. I only used the trailer one time since then and the van is heavier than the trailer so it stops the trailer without the trailer brakes working.

I fairly recently replaced both wheel hubs. I tested the brakes after and that's when I realized they weren't working.

Since I know I am putting out 12v when the brakes are applied, the problem must be on the trailer side. I'm planning on removing each trailer wheel today and making sure the magnet works when the brakes are applied. If both magnets work, I will see if adjusting the brakes helps.

If the magnets work and the brake adjustment doesn't help, I'll be back for help.
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Old 11-06-2019, 07:10 AM   #7
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They don't work.

....
Sounds like you are on the right track.

But one thing.. you said the voltage at the 7 pin was 2 volts without the brakes applied? I'm thinking it should zero, unless there is a stationary hold as described above.
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Old 11-06-2019, 11:18 AM   #8
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Name: Wayne & Barbara
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A simple test is to try the brakes on a quiet road.
drive ahead slowly, and apply the manual override without touching the brake pedal. you should feel the rig slowing.
If it pulls to one side, it may be just one trailer brake is working.

When everything is working right, the trailer brakes should not lock up the wheels.
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Old 11-06-2019, 11:41 AM   #9
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Originally Posted by Wayne Collins View Post
A simple test is to try the brakes on a quiet road.
drive ahead slowly, and apply the manual override without touching the brake pedal. you should feel the rig slowing.
If it pulls to one side, it may be just one trailer brake is working.

When everything is working right, the trailer brakes should not lock up the wheels.
I'm way past that. No trailer brakes at all when trailer is towed.

Something weird just happened though. The brake controller gave me an error message that I think flashed trailer not connected or something like that. I came inside to get my glasses and when I went back out, the error message was gone. I had left the trailer connected and the tow powered up, so the controller wasn't reinitialized.

I know at least 1 magnet is working (my screwdriver stuck to it), so I am going to try a test drive again. If still not working going to put it in the shop.
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Old 11-06-2019, 12:16 PM   #10
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I give up. I know when I'm beat. Now I at least have a little bit of braking, but it still needs adjusting.

For some reason, I find the simple process of adjusting the brakes to be terribly difficult. Unless you get the trailer fairly high off the ground, it is hard to get behind the wheel far enough that you can see into the little adjustment hole. I can get far enough to see the adjustment with the flashlight, but when I put the screw driver in the hole I can't see the adjustment. I'll think I have adjusted it and spin the tire and obviously I never turned the adjustment wheel (or whatever it's called).
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Old 11-06-2019, 01:23 PM   #11
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My Prodigy controller sends an intermittent signal to the brake circuit and displays a "C" when the circuit is good, indicating "Connected". It also provides a readout that increases when I brake harder since they are proportional.
Are you getting signals like that?
During one trip, I would get a momentary "NC" for "not connected" after each brake application. Pulled the wheels and discovered that the part of the magnet that connects to the drum when magnetized was worn enough to show some of the fine wire windings that made up the electromagnet, and it was shorting against the drum when the brakes were applied.
Got new magnets (as well as auto adjusting brakes) and it solved the problem, so maybe check to see if your magnet(s) is/are worn?
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Old 11-06-2019, 03:08 PM   #12
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No luck so far. Took it to a repair shop. One out of 3 guys knew what he was doing and adjusted the brakes. Still not working right. He even hooked up to his pickup and still hardly any brakes. I was pretty sure the problem wasn't in my tow, but this pretty much proves it's not.

He thought it probably is the magnets, but that is not something they do. Called a repair shop that works on RVs and they will try to work me in next week.

I did get it inspected, just haven't figured out where they put the sticker.
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Old 11-06-2019, 03:27 PM   #13
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Quote:
Originally Posted by Huck View Post
No luck so far. Took it to a repair shop. One out of 3 guys knew what he was doing and adjusted the brakes. Still not working right. He even hooked up to his pickup and still hardly any brakes. I was pretty sure the problem wasn't in my tow, but this pretty much proves it's not.

He thought it probably is the magnets, but that is not something they do. Called a repair shop that works on RVs and they will try to work me in next week.

I did get it inspected, just haven't figured out where they put the sticker.
If you have a decent volt meter you can check for voltage drops across a connection. Basically what you are doing is looking for a poor connection.

https://www.bing.com/videos/search?q...0A03&FORM=VIRE
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Old 11-06-2019, 04:02 PM   #14
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How many amps?

He thought it probably is the magnets, but that is not something they do. Called a repair shop that works on RVs and they will try to work me in next week.


Have you done the current test? How many amps, also check voltage at the magnet on the wires. You may have a weak ground. The brakes are small and do not do a lot.
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Old 11-06-2019, 05:24 PM   #15
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Have you done the current test? How many amps, also check voltage at the magnet on the wires. You may have a weak ground. The brakes are small and do not do a lot.
If it was summer and the next few days were going to be nice weather, I might attempt it. But being as it's November, best to just get it taken care of by someone that knows what they are doing.

I'm planning on hitting the road in a month or so and need it taken care of. I've got plenty of other stuff to keep me busy.
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Old 11-06-2019, 05:30 PM   #16
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Originally Posted by ThomasC View Post
If you have a decent volt meter you can check for voltage drops across a connection. Basically what you are doing is looking for a poor connection.
...
How are the ground (negative) connections made? Is it through the frame at any point? There could be your problem.

New brake assemblies are not that expensive so if you cant find a wiring issue then it makes sense to just replace the entire brake assembly,
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Old 11-09-2019, 04:32 PM   #17
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Hey.. What sort of problems would come up with a ground point for the brakes on the frame? I have rewired quite a bit of the trailer and have a centralized ground bus for all of the negative connections that is also frame grounded for reference. However, the brakes have a separate ground position right to the frame. It has been like this since I got the trailer and assumed this was normal practice. However, I have also noticed that the wiring is not of equal length to each wheel. So I am going to rectify that situation. Do you think I should abandon the separate brake ground and connect the ground to my main negative buss?
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Old 11-09-2019, 04:38 PM   #18
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of course every thing is bonded to the frame so I can't really see what difference it would make to leave the brakes directly tied to the frame independently. The only thing I can imagine if I leave things the way they are I may end up with a ground loop effect.
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Old 11-09-2019, 05:05 PM   #19
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Brake power

Quote:
Originally Posted by Stephe View Post
I have rewired quite a bit of the trailer and have a centralized ground bus for all of the negative connections that is also frame grounded for reference. Do you think I should abandon the separate brake ground and connect the ground to my main negative buss?

Did you replace the wire to the brakes? They do not need to be the same length, but It needs to be a large wire. I see no problem with separate brake ground or/and hooking the negative wire and the frame to the same points.
Also, until we know the voltage at the brake back plate and current measurements everything’s a guess.The voltage X the current is the power you get.
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Old 11-09-2019, 05:30 PM   #20
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Hey.. What sort of problems would come up with a ground point for the brakes on the frame? ...
Corrosion on the exposed connection causing a break or at least a loss of electrical conductivity. Its a common problem.

If you run wire that is electrically in parallel to the frame then if the frame connection fails it does not matter. The separate wire will carry the current. Its just redundant.

Ground loop and wire length (within anything even remotely close to reasonable) are not a concern for the brakes.
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