1. A photo-coupled control apparatus for vehicle auxiliary lighting system, comprising: a combination of a photo coupling set includes a control light emitter assembly and a control light sensor assembly, said control light emitter assembly being attached to a location on a surface of a windshield of said vehicle and having a light emitting device for emitting light signals, and said control light sensor assembly being attached to an outer surface of said windshield at a location opposite the location of said control light emitter assembly across said windshield and having a light sensing device for receiving said light signals emitted by the light emitting device of said control light emitter assembly; a switch connected to a battery of said vehicle for providing electric power to said light emitting device of said control light emitter assembly, whereby turning on of said switch emits said light signals; and a control module coupled to said control light sensor assembly, the battery of said vehicle, and lamps of said auxiliary lighting systems, upon turning on of said switch, said light emitting device of said control light emitter assembly emits said light signals so as to be received by the light sensing device of said control light sensor assembly, said control light sensor assembly issuing a control signal to said control module upon receiving said light signals, whereby said control module providing electric power of said battery to said lamps of said auxiliary lighting system for turning on of said lamps.