Troubleshooting trailer ground (weak brakes)

[joshuabardwell]

I did a little more troubleshooting. The brakes look to be spliced into the main hot-wire and ground-wire that runs back along the under-side of the trailer. I hooked up my battery to the brake pin on the connector and measured the voltage across the brakes by sticking the test-meter's leads into the open back-side of the crimp/twist connector holding the splices together. All four brakes had a voltage of about 10.5 volts between their two leads. The battery was putting out just over 12 volts, FWIW (it was starting to run down a bit after all my testing).

I'm not sure where to take the testing from here. If the brake has voltage going through it, but still isn't actuating, what does that mean? Bad magnet? If so, that's surprising given how new the trailer is, and I wonder whether I should take it back to the dealer and ask them to make it right. What do y'all think?

Maybe another step in troubleshooting would be to cut the leads from the bad brake free and hook the battery directly up to them, as opposed to using the trailer's wiring--but I saw voltage on the lines, so I'm not sure that's worth the trouble.

Unfortunately, I have discovered that my test meter does not have an amps function, so I can't measure amp draw to the brakes. How about that? I was really surprised to see that I overlooked that when I bought it.

While I was under there, I noticed that one of the other brake's crimp connectors had come off one of its leads and the only thing keeping it together was the twisted wires. Oops. I'll get right on to fixing that!

Also, I noticed that the leads coming from the brakes were both the exact same color: green and black striped. That surprised me, and it left me wondering whether it doesn't matter which one is hot and which one is ground. Is that the case?

 

[Diamondpilot]

Sounds like a bad magnet.

The brake wires mean its a 3,500# axles, green wires. They color code the magnets this way.

You have a bad magnet. I am about 100% they will not warranty a magnet since its a electrical component. They are cheap, about $20 or so. Just get a new one. As for the wiring it does not matter which wire is positive or negative.

Now for the voltage loss. What size is the wiring on the trailer? It should be 12 ga minimum. I am in the trailer business and see cheap wiring jobs all the time. Small wire will cause lots of resistance and this will lead to low amps and voltage. But if it was working ok before I would just fix the magnet and get your Dodge Controller looked at and go from there.

By the way, dont feel bad. One of my customers bought a $50,000 5th wheel and he complained about weak brakes. When I got looking at it there was something like 18 or 16ga wire for the brakes and a 25' run. Way undersized. I rewired it with 10ga due to the length and axle/brake size and now they are twice as strong.


Chris

 

[horsepuller]

Looks like you are making a lot of progress.

I suggest you make one more electrical test on the wires leading to the bad brake. Try stabbing through the insulation on the brake side of the two leads to the magnet, and read the voltage there. This is necessary because there may be proper voltage at the last junctions, but the junctions themselves could be the problem; there may be no, or some lesser voltage downstream of these (potentially bad) connections.

 

[joshuabardwell]

Sounds like a bad magnet. The brake wires mean its a 3,500# axles, green wires. They color code the magnets this way.

Fascinating.

You have a bad magnet. I am about 100% they will not warranty a magnet since its a electrical component. They are cheap, about $20 or so. Just get a new one. As for the wiring it does not matter which wire is positive or negative.

For only $20, it's not worth the hassle with the dealer.

Now for the voltage loss. What size is the wiring on the trailer? It should be 12 ga minimum.

I don't see any size marking on it, but I did notice that the two wires that the brakes are spliced into are a good bit thicker than the wires that the lights are running off of, so it would seem that whomever made the trailer (Currahee, FWIW) is thinking along the same lines you are. If I had an amps function on my multimeter, I could check the current draw, but since I don't, I think I'll hold off on rewiring my whole trailer until some other projects are out of the way

 

[joshuabardwell]

Looks like you are making a lot of progress.

I suggest you make one more electrical test on the wires leading to the bad brake. Try stabbing through the insulation on the brake side of the two leads to the magnet, and read the voltage there.

That's a good idea--thanks much. Somebody upthread (maybe it was you) mentioned this, but when I saw that the splice was easily accessible, I figured I'd saved myself the trouble.

 

[RobertN]

http://dexteraxle.com/i/u/6149609/f/6-8K_Service_Manual_1-12/Electric_Brakes_1-12.pdf

Note wire size, as Diamond_Pilot mentions

 

[joshuabardwell]

I was talking with my dad about this issue just now, and he pointed out something that seems so obvious that it makes me wonder whether there's a fault that I'm missing. Amps = Volts / Ohms, right? We know the voltage driving the brake magnet (about 12-13 volts, but it can be measured accurately off the hot wire going into the brake). So can't I measure the amp draw of the magnet simply by measuring the resistance across it? And not even need an ammeter function on my multimeter?

 

[3930dave]

Ohms Law can usually be counted on, but a catch with diagnosing automotive wiring is connection quality/integrity.

With an Ammeter in series, you are definitely reading DC current at that point in time (may change/drift a bit, as magnets heat up, battery drops.... but is fairly accurate).

Using a standard multimeter to test for resistance, you (well, the meter actually) end up injecting a very low current. The meter reads the corresponding circuit voltage, does some math, and gives you a resistance reading.

If you have a bad connection (not open, but a little corroded), that connection may pass the tiny bit of current a resistance reading takes (give or take), but will start dropping larger amounts of voltage as you get into the couple of amps per magnet range that the brakes use.

The traditional way to measure current with a voltmeter is to use a calibrated shunt (essentially a high accuracy low value resistance - much less than 1 ohm) in series with the circuit you want to test and measure the voltage across the shunt. Ohms law is accurate, using this setup.

For what I think you have to work with, I'd set up a battery to inject voltage into the brake circuit, ideally with a battery charger to keep it topped up/consistent. I'd then use the voltmeter to check the cable runs (series sections, hopefully that makes sense to you) for voltage drops - voltage will scale up with resistance, either from undersized wire, or corroded connections.

Most low cost meters struggle to measure really low resistances well. Let's say you have a slightly corroded connection that adds 0.3 0hms into the brake magnet circuit. Ballpark the magnets at 2.5 amps each, and that circuit should draw 10 amps for four magnets.

Back to Ohms law - that 0.3 Ohm corroded connection will drop 10 amps times 0.3 Ohms, or in other words 3.0 volts. (Various things are estimated here, just to illustrate the point).

An extra 0.3 ohm resistance is not easy to measure, with a regular hardware store multimeter. That 3.0 volt faulty voltage drop is much easier to measure.

Hope that helps. Rgds, D.

 

[joshuabardwell]

Well, folks, it's time to put this one to bed. It's definitely a bad magnet. The final test was to pull the leads to the magnet and hook up the 12-volt battery directly to them. Nada. I don't think it gets much more definitive than that.

Times like this, I'm glad my trailer came with brakes on both axles, instead of just one, because I can still use it if I need to until I get around to putting the new part in.

I don't suppose there's any reason to disconnect the brake on that axle on the other side, to prevent any pull when braking? I mean, I suppose probably not, since I bet this brake hasn't worked since I got the trailer, and I never noticed any issue before :laughing:

Thanks much for the assistance!

PS: I got a year warranty on the trailer, and to my reading of the warranty, the magnet should be covered, so I'm going to give it a go.

 

[joshuabardwell]

So. Irritated.

I called the place that sold me the trailer and asked about the warranty. I said, "The short version is that I did a bunch of troubleshooting, and the last step was to disconnect the leads going into the brake and hook a 12-volt battery up to it, and it didn't work." The guy started up with, "Well, I don't know if that'd be covered, because it might be something you did while you were troubleshooting, you know, cutting wires and stuff."

I said, "I didn't cut any wires. I just took the wire nuts off the splice and disconnected it. And anyway, the first step in the troubleshoot was to hook the trailer up to the truck and press the brake activation lever on the controller, and the brake didn't work. So nothing I did messed it up, because all I've done with it is tow it for 300 miles or so. Now if you're telling me a magnet would wear out after 300 miles, that's one thing, but I don't think they wear out that fast."

Then the guy says, "I've never had a magnet go bad." Okay. So you've just indicated that you're dumber than I am on this topic, and I'm pretty dumb.

Anyway, he keeps going on about how we can set up an appointment, but if it was something I did, it won't be covered, and I said, "I'm feeling some push-back from you on this, and if that's the way it's going to be, I'll just replace the thing myself. I just wanted to see--the trailer has a one year warranty, and I wanted to see if I could save myself the hassle and have it repaired under warranty like I would expect."

He said, "You can call it whatever you want. It's not push-back. It's just not going to be covered if you messed it up."

I said, "I think it can go without saying that if I messed it up, it's not going to be covered. We don't need to keep waving that flag."

So, anyway, I said, "Well, I've got an errand to run this week with it, but I'll bring it in some time next week and you can have a look at it." And he says, "Well, you can't just bring it in. You need to make an appointment. Our service guy isn't here all day." Okay. Whatever. Can I drop it off? I wasn't expecting you to like look at it while I was standing there breathing down your neck? More push-back.

When I call for warranty service, and the first thing you say is to suggest that I messed the thing up in my troubleshooting. that is the definition of push-back. Just say, "All right. Bring it in and we'll take a look at it." Why are you going out of your way to piss me off? I mean, if it's a covered repair, the manufacturer will reimburse you, right, so it's easy money, right?

Honestly, I now have zero interest in taking it in to them for repair.