A brake controller is an electronic device that allows the driver of the tow vehicle to control the braking power of the trailer from inside the vehicle. If you have a trailer with brakes, then you need a brake controller to make those brakes function. All tandem axle trailers are required to have brakes on at least one axle, and some state-specific laws may require both axles to have brakes. Lastly, all single axles trailers rated at or above 3,000 lbs GVWR are required to have a brake axle.
Brake controllers work through controlling gain. Gain is the measurement of braking force electronically sent to the trailer when the driver steps on the brake pedal of the tow vehicle. Gain is adjustable through the brake controller. It is recommended to adjust your gain prior to driving. Once you start moving, you can make fine-tuned adjustments to ensure you have a proper towing experience.