If your trailer has a break-away switch, it likely has a weak or dead battery, or, it's not set up correctly.
Let me explain what a break-away switch does. If your trailer has a break-away switch, it has electric brakes. If it has electric brakes and the trailer comes off the ball, there would be no power to the brakes if the trailer plug pulled out of the trailer wiring receptacle on the tow vehicle. If you were to try and stop with detached wiring, the trailer tongue would take a dive under the back of the tow vehicle, and the trailer body would slam into the tow vehicle with great force.
If the safety chains stayed attached, there is a myriad of outcomes, none of them good without working trailer brakes, unless you have a battery-powered break-away system. Electric trailer brakes use a powerful electro-magnet on each brake assembly to magnetically move a lever that can generate force equal to the strength of hydraulic brakes. The moving lever provides a mechanical advantage that pushes brake shoes outward to rub on the inside of the brake drums. This creates friction, which slows the rotation of the drums and tires, bringing you to a controlled stop.
The way to stop a trailer that comes off the ball is to activate the trailer brakes, only. This effectively drags the tow vehicle to a controlled stop, all the while keeping the trailer the chain's length from the tow vehicle. The brakes will remain engaged until the on-board battery drains or the activator key is reinstalled. The battery supplied with many new breakaway kits has a charging circuit, but the trailer has to be used frequently to keep it charged off the tow vehicle. Most people don't think about their trailer battery, so most systems simply don't work or perform poorly when you need them the most.
The breakaway switch itself couldn't be simpler. There's a plunger that, when pushed in and latched, physically pushes apart two heavy-duty electrical contacts that slam into each other when the tow vehicle moves some distance from the trailer and pulls the plunger out. The switch has two wires, each connected to a contact inside the switch. The separated contacts keep current from flowing until the plunger is pulled out in an emergency. One wire runs to the positive terminal of the on-board battery, and the unenergized wire runs to the brake wire for all the magnetic brake activators.
The negative side of the battery is typically just grounded to the frame as are many electric brake assemblies. Since trailers and RVs are exposed to weather an auxiliary ground should be added since corrosion can affect how much current can flow through the frame. These connections are usually the weak link and will heat up and lose the capacity to carry current to the magnetic coil in the brake assembly. The performance of that magnet is directly proportional to how much electricity can flow through a ground connection and all the wiring. Resistance could be a safety concern.
Note: the switch is not that small. I wear a XXXL glove.
The break-away switch is mounted to the trailer tongue. I mount it on a swivel for variable angles of pull.
The vinyl-covered wire rope that comes in a kit with no instructions assumes you know what you are doing. It comes with a factory-crimped lead that would lead 99 percent of DIYers to make a possibly deadly mistake. Many professional builders will deliver trailers with no instructions on how to finish the installation. If this cable were used in this factory-finished length, your trailer would never activate the brakes unless the chains broke, and all bets are off as the trailer will seek its own path. That never ends well, ever, brakes or no brakes.
The loop length should be determined with chains fully extended. If the loop is four inches shorter than the chains and attached to the tow hook loops, the plunger will pull out of the break-away switch and activate the electric brakes just about the time the chains go taut. With the trailer brakes activated, the trailer brakes will keep the distance between the trailer and tow vehicle a constant, which should allow you to safely pull off the road. Allowing the trailer to stop the tow vehicle will prevent the impact that inertia would cause if the tow vehicle were to stop with its own brakes. A body in motion tends to stay in motion, even with the brakes on.
With the plunger pulled, current will flow through the break-away switch and flow through the trailer wires to the magnetic coils in the brakes. Magnetic coils are simple machines that convert electricity to magnetism by wrapping a long wire around an iron core. That current flows in one end of the coil and out the other end which flows to the negative side of the battery where it is pushed out again in an endless cycle that’s only broken by the re-installation of the plunger, separating the contacts. If the battery goes dead, it’s going to roll, so chocking the tires is essential to stabilize a detached trailer.
If you have this type of system, it’s very important to check the weak links before you travel. If your battery is over three years old or has bulged, replace it. If the charging circuit isn’t working, it’s cheaper to replace the whole kit. If you don’t know how old the kit is, replace it and add an auxiliary ground. Don’t rely on the chassis as a reliable current-carrying conductor. Sand perfectly flat surfaces at all connections, and use stainless machine screws and star washers with a dialectic grease to keep the connection from corroding. Clean all battery connections for maximum performance. It’s all about flowing electrons.
If you ever find yourself in a runaway situation where you can’t control a wag or a down-hill trailer/tow-vehicle instability, try to remember that the trailer brakes can snap you out of a wag if they are applied from the controller in the manner described above. I found myself in that situation. I was a novice when I lost control of our Spartan Toybox. On the maiden trip I found myself changing from one freeway to another. When I crested the roadway, one leg of the weight-equalizing hitch fell out of its socket. The other remained, pulling on the trailer in abnormal ways. Fortunately, the roadway was four lanes wide at the interchange, and we used every bit of it, wagging four times so hard that I saw the whole trailer in side view mirrors several times.
My 35-foot trailer wagged so hard that the two-inch square stinger bent up and over to one side by 15 degrees in both directions. The F-450 almost went over once or twice. The only thing that saved us was the knowledge that I could stop this catastrophe from getting any worse. I applied the trailer brakes independently through the controller at my knee. It didn’t work fast enough and I had to take my hand away from the controller. By the time I could get back on the controller, I had instant brakes that snapped us straight, headed at a ravine with a guardrail. The brakes slowed me down and I regained control of the pair, but smashed the box of the truck and the back third of the trailer, sideswiping the guard rail with the Porsche in the back.