Section 25253 Of Article 7. Flashing And Colored Lights From California Vehicle Code >> Division 12. >> Chapter 2. >> Article 7.

. (a) Tow trucks used to tow disabled vehicles shall be equipped with flashing amber warning lamps. This subdivision does not apply to a tractor-trailer combination.
  (b) Tow trucks may display flashing amber warning lamps while providing service to a disabled vehicle. A flashing amber warning lamp upon a tow truck may be displayed to the rear when the tow truck is towing a vehicle and moving at a speed slower than the normal flow of traffic.
  (c) A tow truck shall not display flashing amber warning lamps on a freeway except when an unusual traffic hazard or extreme hazard exists.