S.C. Code Regs. 38-393.48. Brakes to be operative

(a) General rule. Except as provided in paragraphs (b) and (c), all brakes with which a motor vehicle is equipped must at all times be capable of operating. (b) Devices to reduce or remove front wheel braking effort. A motor vehicle may be equipped with a device to reduce the braking effort upon its front wheels or, in the case of a three axle truck or truck tractor manufactured before March 1, 1975, to remove the braking effort upon its front wheels, if that device conforms to, and is used in compliance with, the rules in paragraph (b) (1) or (2). (1) Manually operated devices. A manually operated device to reduce or remove the front wheel braking effort must not be (i) Installed in a motor vehicle other than a truck, or truck tractor; or (ii) Installed in a truck, or truck tractor manufactured after February 28, 1975; or (iii) Used in the reduced mode except when the vehicle is operating under adverse conditions such as wet, snowy, or icy roads. (2) Automatic devices. An automatic device to reduce the front wheel braking effort by up to 50 percent of the normal braking force, regardless of whether or not antilock system failure has occurred on any axle, must not (i) Be operable by the driver except upon application of the control that activates the braking system; and (ii) Be operable when the pressure that transmits brake control application force exceeds (A) 85 psig on air mechanical braking systems; or (B) 85 percent of the maximum system pressure in the case of vehicles utilizing other than compressed air. (c) Towed vehicle. Paragraph (a) does not apply to (1) A disabled vehicle being towed; or (2) A vehicle being towed in a driveaway towaway operation which is exempt from the general rule of 38-393.42 under paragraph (b) of that regulation.