Every motorcycle manufactured and first registered on and after January 1, 1978, shall be equipped with at least one and not more than two headlamps which automatically turn on when the engine of the motorcycle is started and which remain lighted as long as the engine is running. This section does not preclude equipping motorcycles used as authorized emergency vehicles with a switch to be used to turn off the headlamp during emergency situations or when the light would interfere with law enforcement, if the switch is removed prior to resale of the motorcycle.