If motor and other vehicles are operated in combination when lights are required, any lamp, except tail lamps, need not be lighted if the lamp would be obscured by another vehicle of the combination by reason of its location on a vehicle of the combination. This section does not affect the requirement that lighted clearance lamps be displayed on the front of the foremost vehicle required to have clearance lamps or that all lights required on the rear of the rearmost vehicle of any combination be lighted.