A lighting unit comprising a plurality of lighting loads arranged in various parts of a vehicle, a first control device that outputs a control signal for controlling the plurality of lighting loads independently, and a wire harness assembly configured to connect the plurality of lighting loads to the first control device, said wire harness assembly comprising: a first wire harness connected to the first control device and including a power-supply line, a ground line, and a signal line configured to multiplex transmission of the control signal outputted from the first control device to each of the lighting loads; a second wire harness including a first electric line commonly connected to one ends of the plurality of lighting loads, and a plurality of second electric lines connected to the other ends of the plurality of lighting loads respectively; and a relay connector connecting the first wire harness to the second wire harness, and including a second control device configured to control power supply to each of the lighting loads in accordance with the control signal transmitted from the first control device, wherein the relay connector includes an outer housing, a plurality of terminal fittings (55, 56, 57, 58, 59) accommodated in the outer housing, the terminal fittings being respectively connected to the power-supply line, the ground line, the signal line, the first electric line and the plurality of second electrical lines, and the second control device accommodated in the outer housing, characterized in that the each of the lighting loads includes a plurality of light sources (21, 22, 23) emitting colors different from each other, wherein the plurality of second electric lines are respectively connected to the other ends of the light sources (21, 22, 23), wherein the second control device controls power supply to each of the light sources (21, 22, 23) so as to emit a lighting color in accordance with the control signal transmitted from the first control device, and the lighting loads are arranged anywhere inside the vehicle. a first wire harness connected to the first control device and including a power-supply line, a ground line, and a signal line configured to multiplex transmission of the control signal outputted from the first control device to each of the lighting loads; a second wire harness including a first electric line commonly connected to one ends of the plurality of lighting loads, and a plurality of second electric lines connected to the other ends of the plurality of lighting loads respectively; and a relay connector connecting the first wire harness to the second wire harness, and including a second control device configured to control power supply to each of the lighting loads in accordance with the control signal transmitted from the first control device, wherein the relay connector includes an outer housing, a plurality of terminal fittings (55, 56, 57, 58, 59) accommodated in the outer housing, the terminal fittings being respectively connected to the power-supply line, the ground line, the signal line, the first electric line and the plurality of second electrical lines, and the second control device accommodated in the outer housing, characterized in that the each of the lighting loads includes a plurality of light sources (21, 22, 23) emitting colors different from each other, wherein the plurality of second electric lines are respectively connected to the other ends of the light sources (21, 22, 23), wherein the second control device controls power supply to each of the light sources (21, 22, 23) so as to emit a lighting color in accordance with the control signal transmitted from the first control device, and the lighting loads are arranged anywhere inside the vehicle.