Section 24602 Of Article 3. Rear Lighting Equipment From California Vehicle Code >> Division 12. >> Chapter 2. >> Article 3.

. (a) A vehicle may be equipped with not more than two red fog taillamps mounted on the rear which may be lighted, in addition to the required taillamps, only when atmospheric conditions, such as fog, rain, snow, smoke, or dust, reduce the daytime or nighttime visibility of other vehicles to less than 500 feet.
  (b) The lamps authorized under subdivision (a) shall be installed as follows:
  (1) When two lamps are installed, one shall be mounted at the left side and one at the right side at the same level and as close as practical to the sides. When one lamp is installed, it shall be mounted as close as practical to the left side or on the center of the vehicle.
  (2) The lamps shall be mounted not lower than 12 inches nor higher than 60 inches.
  (3) The edge of the lens of the lamp shall be no closer than four inches from the edge of the lens of any stoplamp.
  (4) The lamps shall be wired so they can be turned on only when the headlamps are on and shall have a switch that allows them to be turned off when the headlamps are on.
  (5) A nonflashing amber pilot light that is lighted when the lamps are turned on shall be mounted in a location readily visible to the driver.