...Here is my perception about automobile brake system and trailer hooked up related: 1/ Manual hand brake or emergency brake in an automobile is used by...purely mechanical source which came from..human energy. So it will not affect to brake
light of a car, neither to brake controller for braking a trailer hooked up with the car...2/ Regular brake system of a car is used by...hydraulic system which is activated by either brake pedal depressed or...cruise control activated or any other fancy, automatic sensor system. In this manner, whenever brake
lights of the car are on, by
electrical signal from brake pedal wiring, the
brakes will be applied by hydraulic source in car and also trailer with their e
brakes by
electrical signal...3/ No matter how fancy/automatic brake system of a car has, when its' brake
lights are on, the brake is activated and also ebrake of trailer due to basically parallel connection of trailer ebrake with car brake wiring...I could be wrong though, hopefully get more clarification from brake controller's manufacturers or car dealerships...