When the Brake controller is activated, it sends a DC current from 1 to 12 volts to the trailer brakes. HOW MUCH voltage determines how much trailer braking happens. When you pull the Break a way pin, you supply 12 volts direct to the trailer brakes(lock up) and THAT voltage will also feed back to the brake controller. The Brake Controller may not be able to handle that INPUT voltage from the Trailer and "may" destroy something in the brake controller. In a TRUE trailer break away, even with safety chains, the odds are the 7 way will be pulled out of the truck. As others have stated, IF a break away happens, what remains of your brake controller will not be thought of for days or weeks to come. Doug