A signal indicating when the brakes are applied is provided to the ASC control unit. This signal is used to discontinue ASC regulation, if active, and begin ABS regulation if necessary.
If the brakes are not applied, (switch open), the control unit supplies a monitoring voltage through the brake light circuit. This voltage is pulled low by the ground path supplied through the completed brake light circuit.
A voltage is supplied to the control unit with the brakes applied, (switch closed), electrically removing the ground circuit and producing a high signal.