New Jersey Statutes Title 39. Motor Vehicles and Traffic Regulation 39 § 3-54.16

All red emergency lights shall be mounted on the exterior of the motor vehicle. No more than two red emergency warning lights shall be installed on a vehicle. If one light is used it shall be installed in the center of the roof of the vehicle, or on the left windshield column in a position where a spotlight is normally located. If two lights are used they may be placed on the windshield columns on each side of the vehicle where spotlights are normally mounted, or on either side of the roof at the front of the vehicle directly back of the top of the windshield. Under no circumstances may one light be placed on the roof and one on a windshield column in the spotlight position. They shall be operated only while the vehicle is being used by the registered owner chief or first assistant chief in answering a fire or emergency call.