Washington Revised Code Title 46. Motor Vehicles § 46.37.050. Tail lamps

(1) After January 1, 1964, every motor vehicle, trailer, cargo extension, semitrailer, and pole trailer, and any other vehicle which is being drawn at the end of a combination of vehicles, shall be equipped with at least two tail lamps mounted on the rear, which, when lighted as required in RCW 46.37.020, shall emit a red light plainly visible from a distance of one thousand feet to the rear, except that passenger cars manufactured or assembled prior to January 1, 1939, shall have at least one tail lamp. On a combination of vehicles only the tail lamps on the rearmost vehicle need actually be seen from the distance specified. On vehicles equipped with more than one tail lamp, the lamps shall be mounted on the same level and as widely spaced laterally as practicable.

(2) Every tail lamp upon every vehicle shall be located at a height of not more than seventy-two inches nor less than fifteen inches.

(3) Either a tail lamp or a separate lamp shall be so constructed and placed as to illuminate with a white light the rear registration plate and render it clearly legible from a distance of fifty feet to the rear. Any tail lamp or tail lamps, together with any separate lamp or lamps for illuminating the rear registration plate, shall be so wired as to be lighted whenever the head lamps or auxiliary driving lamps are lighted.