After-market, detachable warning lights for a reversible highway sign are easily attachable to existing stop/slow highway signs currently in use in highway construction areas. Left and right light boxes are attached to opposite vertical edges of the sign with a pair of red lights on the "stop" side of the sign and a pair of yellow lights on the "slow" side of the sign. A multi-functional switch enables the workman to create a variety of lighting conditions. These conditions could include red and yellow constantly ON; red and yellow blinking; red and yellow strobing slowly; and red and yellow strobing rapidly. In addition, the switch enables the workman to put either set of lights in a particular independent mode thus increasing the variation of the lighting system. For example, the red lights may utilize a constant ON mode while the yellow lights could be slowly strobing. The sign and pole have internal wiring and are supported by a lower base with wheels. The twelve-volt battery supply rides on the base. The sign is readily moved from site to site and allows the workman to select many different combinations of lighting effects.