Electric trailer brakes stopped working

[RamFP620]

I recently installed the OEM brake controller on my 2017 1500 Big Horn. I did a test run back then with the trailer that I will be pulling and everything worked great. Today, I hooked up and as I pulled away I manually activated the brakes to make sure they worked...all was ok. While sitting at a traffic light, I felt a jerk of the trailer and then noticed the alert that the trailer is no longer connected.....so I'm guessing the jerk was the trailer rolling back/relaxing because the brakes released.
I checked the trailer plug, removed it, re-inserted it, no good...brakes still didn't work. All trailer lights still worked.

I checked the 30 amp fuse for the Integrated Trailer Module, it was good. I voltage checked the pin in the trailer plug on the truck and it was outputing around 8v at 100%. I'm guessing it was 8v because my gain was set to 6.5. Assuming my understanding of output voltage vs gain is correct, it appears nothing is wrong on the truck end.

Since I'm new to electric brakes, is it a straight connection from trailer plug to brakes? Are there typically any fuses in the middle on the trailer or some other device between the actual brakes and the trailer plug? I'm sure the next step is to test/check something on the trailer, but not sure what.

 

[04fxdwgi]

There are typically no fuses on the trailer itself. Do you have a wiring breakout box on the trailer?
If you have voltage coming in and stuff is still dead, I would be giving the grounds connections some love, on the trailer and the truck.. Bad grounds make all kinds of F*U*B*A*R stuff happen on vehicles, especially these rolling computers.

Something like this.



Great for point testing the trailer wiring. Here is how they are wired.

 

[BossHogg]

I checked the trailer plug, removed it, re-inserted it, no good...brakes still didn't work. All trailer lights still worked.

I checked the 30 amp fuse for the Integrated Trailer Module, it was good. I voltage checked the pin in the trailer plug on the truck and it was outputing around 8v at 100%. I'm guessing it was 8v because my gain was set to 6.5. Assuming my understanding of output voltage vs gain is correct, it appears nothing is wrong on the truck end.

Because the trailer brake circuit is a pulse width modulated signal (you can look up PWM for an understanding) and is never driven at 100% on, your DVM will read the effective DC voltage (voltage times the percentage of duty cycle on time, e.g. 50% * 12 = 6volts) of the signal so 8 volts is right about what it should read. I'm assuming your trailer uses electromagnetic brakes, if you have access to a DC clamp meter, measure the amp draw on the trailer brake wire, each wheel with a brake will pull about 3 amps.

Modern brake controllers send a short periodic PWM signal and then sample the brake line to see if any current is being consumed, this is how the brake controller knows there is a trailer with brakes connected. This would narrow the issue down to a ground issue, a connector issue, or a brake wiring issue.

Just an FYI, some DVMs, usually the more expensive ones but not so much anymore, will measure and report the RMS of a pulse signal. In the case of measuring the voltage of a brake wire, effective voltage versus RMS is about the same in a DC circuit.

 

[2003F350]

Above is good advice on how to troubleshoot the issue. If you're getting a signal of any kind from the truck, then you're correct, things sound good on the truck end.

Depending on how your trailer was wired, it may or may not have a junction box as pictured above. Having it makes things a bit easier to troubleshoot, and allows you to rule out the plug side, but it's not necessary to have.

To me it sounds like a ground issue, which is pretty common on trailers. Let's face it, most people don't wash their trailers, especially flatbeds or enclosed trailers (they're a bit better when it comes to RVs), so stuff builds up over time and causes grounds to fail.

Troubleshooting electric brake issues can be a pain and usually means you need to crawl around under the trailer inspecting wires.

 

[RamFP620]

There is a box up by the tongue but it doesn't quite look like a junction box...maybe it has the battery in it....I will take a peek.

I'm assuming then it's probably a failure at a common point since all 4 brakes don't work. This also assumes the ground/negative side of each brake doesn't just connect to the trailer frame and that it all goes back to the junction box.

Thanks for the help and I'll see what I see when I look at it later today.

 

[2003F350]

There is a box up by the tongue but it doesn't quite look like a junction box...maybe it has the battery in it....I will take a peek.

I'm assuming then it's probably a failure at a common point since all 4 brakes don't work. This also assumes the ground/negative side of each brake doesn't just connect to the trailer frame and that it all goes back to the junction box.

Thanks for the help and I'll see what I see when I look at it later today.

That box may be the battery for the breakaway system, you may not have a junction box (my flatbed only had the battery box, it didn't have the junction box until I upgraded the plug and got one very similar to what is posted above). In that case the wires run from the plug to their final destinations (lights, brakes, etc).

If the trailer lights are still working properly (turn signals, running lights, brake lights) then the plug is grounded properly to the frame, as are the lights. This narrows you down to JUST the brake circuit. Depending on how your breakaway battery is hooked in, it COULD be that those wires have corroded and caused you to lose the trailer brakes. It could also be the connection where the single power wire splits to your brakes, I don't know if you have 1 or 2 axles, some trailers only have brakes on one axle, others (usually higher GVW trailers) have brakes on both axles.

Sounds like you're going to be chasing wires.

 

[dsherman26]

You could try setting your meter to measure resistance and probing between pins 1 and 2 on the trailer connector, you should measure something around 1-2 ohms. My travel trailer had the unfortunate incident of bottoming out on one side, and the builders stupidly ran the brake wires between the axle and the frame. Well, the u-bolt on the axle left a dimple in the frame, and neatly pinched the brake wires, cutting them. Brake controller wasn't damaged, thankfully, but I was scratching my head how my 1 year old trailer suddenly had no brakes as I was getting ready to go camping, so the wife patiently waited while I did an emergency repair of the brake wires in my driveway.

 

[RamFP620]

You could try setting your meter to measure resistance and probing between pins 1 and 2 on the trailer connector, you should measure something around 1-2 ohms.

Back to the trailer I went today. This is tandem axle box trailer with brakes on all fours. To add a little clarification, this trailer is the schools band trailer and I'm trying to see if there's something stupidly obvious to fix otherwise the school needs to take it to the professionals. I'm an electrical/electronics kind of guy and I'm sure I could fix it but the little word "liability" comes to mind.

I opened the box and yep there was the battery laying on top of all the wire nutted connections between the trailer plug cable and the trailer wiring. I guess it's what ever the cheapest way to build trailers these days With the trailer plug disconnected, the battery was at 12.5v.... seems good to me.
For the brake wiring, there was enough of bare copper exposed under the wire nut that I could stick the meter probe on and confirmed the same 8 volts to that point. Following the cabling under the trailer, the brakes are daisy chained which I guess makes sense....cheapest way to wire it.
Continued with the resistance test and I was getting readings in the kohms and from google and dsherman26'a post that obviously is not right. So it looks like there is a wiring fault somewhere causing a high impedance.
One thing I noticed was the wiring to the break away switch was run through the batt box with no grommet to protect the wire from the plastic edges of the box. Could the break away switch cause such a problem?

It just blows my mind, I guess because I'm new to electric brakes, all I was doing was sitting at the traffic light and it all died.

Thanks again for all the help so far.

 

[04fxdwgi]

One thing to be considering, the brake wire goes to the brake coil. The coil is then connected to the frame ground somewhere. I have see some (which I repaired) grounded with just a sheet metal screw into steel / aluminum someplace. Seen one grounded to the brake backing plate (bad idea). That ground wire needs to go a solid, clean connection on the frame with a good fastener, like a bolt with a flat and lock washer and then coated to prevent corrosion.

Breakaway will not do what you are seeing. It sets the brakes from little battery when pin is pulled and it closes. Does nothing in the open position.

Also, using wirenuts in any application on a vehicle / trailer / boat is a big no-no. They WILL corrode and being under battery is even worse. Use bare crimp connectors and sealing heat shrink tube for a reliable / waterproof connection.

 

[crash68]

Could the break away switch cause such a problem?

The trailer brake circuit runs through the break-away switch, it will apply +12V from that battery to the trailer brakes when the switch is pulled.

 

[RamFP620]

One thing to be considering, the brake wire goes to the brake coil. The coil is then connected to the frame ground somewhere. I have see some (which I repaired) grounded with just a sheet metal screw into steel / aluminum someplace. Seen one grounded to the brake backing plate (bad idea). That ground wire needs to go a solid, clean connection on the frame with a good fastener, like a bolt with a flat and lock washer and then coated to prevent corrosion.

Breakaway will not do what you are seeing. It sets the brakes from little battery when pin is pulled and it closes. Does nothing in the open position.

Also, using wirenuts in any application on a vehicle / trailer / boat is a big no-no. They WILL corrode and being under battery is even worse. Use bare crimp connectors and sealing heat shrink tube for a reliable / waterproof connection.

I guess the one good thing was that the brake wiring used a 2 conductor cable to carry the 12v and ground to each brake. Nothing was tied to the frame.

I agree with you on the wirenuts....I was surprised to see that.

Thanks for the info.

 

[62Blazer]

Double check all the grounds. From my experience the majority of electrical problems on a trailer are from ground related issues. As you probably know the ground is not an all or nothing type of thing. If you have some ground, but a poor connection, it may be enough for the lights to work but the brakes pull a lot more amps and thus require more grounding.
As far as the brake issue starting while you were sitting at a light that is quite feasible. Assuming you were sitting there with your foot on the brake and thus it was putting power to the brakes at the time.

 

[Divail]

I guess the one good thing was that the brake wiring used a 2 conductor cable to carry the 12v and ground to each brake. Nothing was tied to the frame.

I agree with you on the wirenuts....I was surprised to see that.

Thanks for the info.

Hi, I have a 2024 RAM 3500 and I'm experiencing the same issue. Today, I tried using a different trailer, but the brakes still didn't work, which leads me to believe that the problem is with the truck itself. Have you tried using other trailers to see if their brakes work?

 

[2003F350]

Hi, I have a 2024 RAM 3500 and I'm experiencing the same issue. Today, I tried using a different trailer, but the brakes still didn't work, which leads me to believe that the problem is with the truck itself. Have you tried using other trailers to see if their brakes work?

Yours I would not touch, I'd send it back to the dealer for them to figure out. You should be absolutely under warranty unless you use it for hot-shot use.