As a long time listener, this is probably the third time in as many years as I've heard Tom say he has no idea how electric brakes work. This is the simplest explanation I can offer. Imagine the trailer has drum brakes with an emergency brake cable and handle that come up all the way to the car. When you step on the car brakes you simultaneously pull the handle to give pressure to the trailer brakes. Now, take away the handle and the cable and replace the cable mount inside the drum with a pivot arm with a small electromagnet mounted on. The handle in the car is replaced with a DC servo control that is connected to the vehicle brakes. The servo gives a varying amount of DC power to the electromagnet. The magnet then starts to cling to the inside of the steel drum, providing resistance and pushing the pads out to slow the trailer. The servo provides varying power so that you are not just turning the magnet on full and totally locking up the wheels. There is no motor drive, as Tom suspects, it is magnetic driven. It sounds like Paul either has a blown bulb (as Tom said) or a loose ground wire and the magnet is grabbing when the signal flashes because the circuit is looking for a replacement ground. Hope that helps!