Abstract: A brake controller for use in a tow vehicle to control the application of towed vehicle brakes. The brake controller is responsive to movement of the tow vehicle brake pedal to send electronic brake control signals to the towed vehicle brakes, actuating the brakes in proportion to the movement of the brake pedal. An optical coupler senses movement of the brake pedal by a graduated increase in transmitted light, or by counting marks associated with a spring-tensioned cable or chain secured between the tow vehicle firewall and the brake pedal arm. A microcontroller is incorporated into the brake controller to adjust the proportionality of the brake actuation in response to operator gain settings, and to allow for manual actuation of the towed vehicle brakes.