Bear with me. Last year coming through WV my truck and trailer brakes got very hot and we had quite the scare. The brakes on the truck got repaired and now onto the trailer. The trailer has 2 axles. It only had brakes on one axle. The rear axle has flanges for backing plates, so I added brakes to the other axle. I rewired both axles with 12 gauge trailer brake wire. The front axle wires come down the left side and piggybacks from left to right. The rear goes down the right and piggybacks from right to left. It is all brought together up front in a junction box. You also have an emergency brake battery on board the trailer. Battery power and ground enter the junction box from the truck (along with all others). Power is jumped to a mini charger for the E brake battery. One wire to the positive of the trailer battery, one to positive from the truck and the other goes to the breakaway switch. From the breakaway switch to the brakes. I got the brakes done and went to burn them in. BARELY any brakes. I turned up the brake control and I have nothing but the left front locking. Back home, I checked all wires and connections. Good. I jacked up the trailer and pulled the breakaway. Nothing but left front, and not fully locking at that. Truck connected or disconnected. I disconnected the trailer battery and tested it. 12.86V. I'll skip a few steps here, I ended up putting my jump box in place of the trailer battery. Truck still disconnected. Pull the breakaway, and I have all 4 brakes. Put the breakaway back in, hook the wire back to the truck and hit the brake control, all 4 brakes. Trailer disconnected, or connected I still have power and ground at the trailer connector on the truck. Which powers the charger for the mini battery. I have power to the charger, and it has a working output for the battery. Everything is working. Except for the battery that still has almost 13V, that I replaced with my jumpbox. I went to the store in utter disbelief. Bought a battery, put it in and the brakes work. I just don't understand. How does the EMERGENCY brake battery play any role in whether or not the applied brakes work? It works, so I'm happy. But I need to understand this. What the heck is going on here. Is this common knowledge and I'm a big dummy? 😆
Electric trailer brakes (drum)
Kefsn
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Your junction box needs a ground to trailer frame I don't see it grounded to trailer frame. That will ground trailer to truck as well. That maybe way its working via the "battery" and charger.
Either way if its working and you can adjust gain and manually lock up all for with switch on controller then its good.
Either way if its working and you can adjust gain and manually lock up all for with switch on controller then its good.
Top right corner of the pic it goes to trailer frame. Sorry, I'm not a very good drawer.
Yes, it does work with adjusting gain and manually. So ultimately I'm happy. I just like to understand things. LOL! And hoping not to have a gremlin, and that someone had run across this before.
See #24.
1955 210 two door post, six cylinder, three on a tree, Navajo Tan and India Ivory
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Someone once showed me a photo on his phone of car that had belonged to someone he knew. It was a high-dollar restoration '56 belair hardtop. The guy was pulling it on a trailer without e-brakes and someone pulled out in front of him. He slammed on his brakes and avoided the car but the trailer swung around and snapped loose from his truck and flipped. The '56 was totally demolished. Brand new restoration - no insurance. It still hurts me to think about it. I added e-brakes (both axles) to my trailer to make sure I don't have a repeat of that with my car, tractor, or anything else. I don't have the break-away switch (and perhaps I should). I've yet to pull my car on it but my son has used it several times to move his tractor. At least once a month I'll slow down to about 40 mph and manually engage the trailer brakes. When I feel the brakes engage and slow the truck down I know the brakes are working. The last time I loaned my trailer it came back with wiring pulled loose and the tongue jack bent. The guy was using a 1 7/8" ball when the tongue was designed for a 2" ball. When he got to the top of my driveway and went thru a dip the jack bottomed out and lifted the trailer off of the ball. Thank goodness that didn't happen while he was on the road with it.
Sorry, I read again. There is one from the junction box to the frame. I forgot that in my illustration. I'm not currently near the trailer. I went from memory. I will double check them for sure when I get home. I feel it has to be ground the more we talk about it.
Read #24. Sorry. I messed up
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If you have a winch you have a battery already you just need the brake away switch. These are normally required by law so check you local laws either way for how cheap they are use one.
The brakes can even be used unloaded just adjust your gain down to 3-4 and you can feel them slowing you down. This helps save your truck breaks as the trailer is heavy alone too. This way you can feel them working all the time.
Reason number 4,503,000 I don't loan my stuff.
You know what.... You may have nailed it. The more I think about it, I cannot say for 100% certain there is one from the junction to frame. 🤔 I will be checking this tonight.
Dang.... I think ya got it...
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Hmmm what was the orginal failure you were worried about? It only working with the breakway pulled?
EDIT if not junction box ground its grounding via hitch to truck. But the battery is grounded via trailer and brakes are getting ground as well via axles still so maybe issue. Can test it out and see.
I think you got it. See #28.
I only had minimal brakes to the LF wheel. That is it. With control all the way up or manually. The LF is also the shortest run of wire.
A trailer I build always has all the wiring run through metal conduct with metal boxes at key points. cheap and protects things. But then it also gets brakes on both axles too.
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this trailer had brakes on both. Built in Iowa and the main wiring is enclosed. where it goes to the wheels is exposed a bit and someone must have drug it through some heavy brush or something because the wires are jerked out at the backing plates. It will all get fixed when it gets a new ft axle or get this one straightened
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Thanks! I believe BO185 may be onto something. I may be "short" a ground. LOL.@Kefsn good luck--when I worked for dealership I HATED intermittent or a one time hiccup in something electrical. I've spent days checking and rechecking for something and IF I finally found it GM only gave 2 hrs diagnostics + whatever the labor time was to repair what I found.
I too have a very small circle of friends I will loan a trailer. Loaning them out never works well for you.
My best guess is that you have a poor connection somewhere and while replacing the battery, you bumped it and it now makes contact. Chances are very good that the problem will return. I hope you aren't pulling a heavy load and have to stop quickly, and suddenly... only 1 wheel has working brakes. Then you
your pants and hopefully that is the worst that will happen and neither you nor anyone else gets injured or killed.
UPDATE : Here is a pic of the junction box.
![Image]()
I found that the nut was tight holding the ground wires, BUT the ground coming from the truck was able to wiggle. I had the connectors staggered weird. Causing the grounds to not tighten fully against each other. (I think it was on the heat shrink.) There was a ground to the trailer, but it was riveted and a whopping 18 gauge. The trailer battery and the trailer frame ground were tied together and then brought to the junction. I think that I lost my ground connection to the brakes through the stud in the box. All brake grounds come to here, not the frame. When I wiggled and jiggled, I must have "fixed" it. I did run a 10 gauge ground from the stud to the frame. And a new one to the battery as well. It still works as of now. Hopefully it stays that way! Thanks all for the input! If I don't make it to the Nationals, y'all know I lost brakes again! 😬
I found that the nut was tight holding the ground wires, BUT the ground coming from the truck was able to wiggle. I had the connectors staggered weird. Causing the grounds to not tighten fully against each other. (I think it was on the heat shrink.) There was a ground to the trailer, but it was riveted and a whopping 18 gauge. The trailer battery and the trailer frame ground were tied together and then brought to the junction. I think that I lost my ground connection to the brakes through the stud in the box. All brake grounds come to here, not the frame. When I wiggled and jiggled, I must have "fixed" it. I did run a 10 gauge ground from the stud to the frame. And a new one to the battery as well. It still works as of now. Hopefully it stays that way! Thanks all for the input! If I don't make it to the Nationals, y'all know I lost brakes again! 😬
We did that last year. SCARY!!! Truth be told, maybe the bad connection was my REAL issue last year... My slack tail never checked until now.My best guess is that you have a poor connection somewhere and while replacing the battery, you bumped it and it now makes contact. Chances are very good that the problem will return. I hope you aren't pulling a heavy load and have to stop quickly, and suddenly... only 1 wheel has working brakes. Then you
1955 210 two door post, six cylinder, three on a tree, Navajo Tan and India Ivory
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I installed a 3rd party controller but used the factory harness. Nothing would work until i added a ground from the backside of the connector in the dash to the metal underneath the dash. Apparently the OEM ground was open.
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