Vehicle Code – VC 24252
VC § 24252. Lighting equipment requirements
(b) The voltage at any tail, stop, license plate, side marker or clearance lamp socket on a vehicle shall not be less than 85 percent of the design voltage of the bulb. Voltage tests shall be conducted with the engine operating.
(c) Two or more lamp or reflector functions may be combined, provided each function subject to requirements established by the department meets such requirements.
(1) No turn signal lamp may be combined optically with a stoplamp unless the stoplamp is extinguished when the turn signal is flashing.
(2) No clearance lamp may be combined optically with any taillamp or identification lamp.