Breakaway Box Puzzles Me

Here's the deal. I bought a new 18' equipment trailer last year and ordered it with a break away kit factory installed. I noticed the other day it would not active the brakes when the pin was pulled. Logically, I took out the battery and fully charged it. Put it back in and same results. I have contact sparks on the contacts inside the breakaway switch when I pry them apart with a screwdriver. Thinking I had a short somewhere, I hooked the trailer plug up to the truck plug (did not latch the ball). The brakes seemed to work like they should and always have. Yes, all four brakes hummed. I was getting something like 1.6 output volts (will go to max brake voltage setting by using the manual brake slider), 1.5 output amps, 12.?? battery volts, and 12.?? brake voltage on my P3 diagnostics. I had it hooked to my newly purchased used truck, so I am not sure these results really reflect the true numbers I was getting before with my other vehicle. As I thought the output volts and amps should be higher when using the truck brake pedal. But the truck was turned off and sitting still. It would take about 3 seconds for the output amps and volts to change, the battery and brake voltage were instant. Although, the trailer brake hum was delayed by the pedal unless I used the manual slider on the controller. I can't remember if that was normal before. Seems like it was.

I even thought the wiring from the breakaway switch to the brake wire splices was bad. So I removed them and checked them. They seemed okay. Put them back on and you can hear an instant click on the brakes, but no humming when you pull the pin. Yes, I removed my trailer/truck plug before pulling the pin to keep from destroying my controller. I even thought I had the wires backwards, so I reversed them. When I pulled the plug, the side marker lights would come on. I thought this was caused by backfeeding into the taillight/parking light wiring. As the brakelights are tied into the brake wiring. So, I switched it back.

My breakaway kit is wired as follows: Switch wire to battery positive. Switch (other wire) to trailer brake wire (spliced in with connector). Battery ground to trailer ground then it also spliced into other brake wire (I assume that is the ground for the brakes).

Any suggestions on where to go now? I have went around and wiggled all the wiring, but the brakes still won't hum with the pin pulled.

I think that the reason the brakes hum when using the controller on the truck is that the controller regulates the voltage by switching it on and off rapidly, kind of creates [square-wave] AC. The battery on the breakaway is just pure DC, so no humming.....
So when you try to measure with an ammeter, the voltage reading is not true. Switch to AC on your tester, I bet that will give you a different reading.

If I remember correctly, when I first bought the trailer and I pulled the pin to verify it did work and the brakes still made the humming sound. I guess I need to hook up the trailer, pull the pin, and pull forward to see if the brakes lock up.

It still puzzles me. Last night I traced every wire and connection and found nothing wrong. I have verified the controller volt and amp readings are correct for the 6.0 volts I had applied to the 4 brakes. After reading the controller manual, it will engage on a 5 second delay at a 25% hold rate if the truck is immobile and turned off. That explains my delay and readings I was getting. I have taken the breakaway switch apart and cleaned the 2 contactors, and even ran new wires for the brake wire tie in. When the pin is pulled, I have verified I have power at the trailer brake wire connection like it is suppose to be. I am beginning to wonder if my battery just doesn't have enough power to kick it on. So, I am going to wire a temporary 12 volt source from my vehicle to the battery wire side of the switch. If the brakes hum then, my battery is bad. If it still does nothing, then I guess it is back to the drawing board.

Pull the pin and measure the voltage at the brakes. That will tell you if they're receiving voltage or not.

Did you check the ground on the battery? Made no mention of it so I thought I'd ask.

I'm glad you are checking and verifying your breakaway unit. I do not even have one on any trailer of mine with electric brakes. I have safety chains on all: bumper and goose neck ball. I have been thinking which is better. The trailer going where ever it pleases or locking up and spinning donuts in the middle of an interstate...

CT

I would check the breakaway battery connects and battery ground. Then pull the pin with the trailer on the truck and try to drive forward, that's how I always check my breakaway brakes.

I have checked the connections and even removed and reattached them. I removed the ground, cleaned it and still no luck. I will try hooking up to the truck and pull forward. I still have not checked the voltage at the wheel brake connection. I don't think I will find anything wrong there either. The brakes work fine with the trailer plug connected.

I am beginning to think I might have a bad battery. It shows a full charge after I charge it up. But, I think when voltage is drawn from it, it doesn't have enough to apply to the brakes. Like an internal battery short. So, I am also going to hook the breakaway power wire to my battery charger and see if it will make the brakes hum then.

You won't hear the brakes "hum" when they're powered directly from a battery. There's nothing in electric brakes except a big electromagnet that's drug along by the rotating wheel and pulls on a lever to expand the shoes. There's nothing in there to "hum".

The "hum" you hear is from the brake controller rapidly pulsing the magnets on and off to control the braking force. It's called "pulse width modulation" and is a much more efficient way of controlling braking force than having a big resistor in the controller to limit current.

Before you spend a bunch more effort, hook the trailer to the hitch but don't connect the electrical plug. Pull the breakaway pin, and the trailer wheels should lock if you try to pull the trailer. If all the wheels that have brakes slide, your breakaway is working fine.

Keith