Brakes and Lights
In all my 56 years I've never heard that one. The electric brake on your trailer is just a big DC electromagnet. Your controller is a variable resistor that applies a different amount of DC Voltage to the trailer magnet that applies the brakes. The switch that activates your brakelights does only that. Light on/Light off. When you press on the brakepedal your controller senses the position of the pedal and sends the amount of voltage that the controller is set to deliver down a wire just for the trailer brakes. Your connecter to the trailer has seperate wires for turnsignals, lights, brakelights, sometimes the turnsignal bulb is used as a brakelight, depending on how yours is setup, often another wire for 12 Volts DC to power your lights inside the trailer from the battery in your coach, and finally, another wire to your electric brakes on your trailer. What a run-on sentence! You need a different trailer guy!
2009 Gulf Stream Endura on the International Chassis. Joe at J&L RV in Fontana, CA did the work for GS and it appears that its finally done right. Seems GS "forgot" 5 seals in the 2 slideouts