S.C. Code Regs. 38-393.19. Requirements for turn signaling systems

(a) Every truck, or truck tractor shall be equipped with a signaling system that in addition to signaling turning movements shall have a switch or combination of switches that will cause the two front turn signals and the two rear turn signals to flash simultaneously as a vehicular traffic hazard warning as required by Regulation 38-392.22 with the ignition on or off. (b) Every semitrailer and full trailer shall be equipped so as to have the two rear turn signals to flash simultaneously with the two front turn signals of the towing vehicle as a vehicular traffic hazard warning as required by Regulation 38-392.22(a).