An improved wiring system is provided in which a connector box having a plurality of terminals, electrical circuitry, and bus bars is incorporated. Since each bus bar provides forked conductive paths between the circuitry and the terminals, the terminals of the connector box and outside connectors can be connected by way of wires in a one-to-one correspondence. This simplified wiring mode greatly reduces manual labor in the manufacture of wire harnesses. Moreover, if a plurality of connector boxes of such structure as above are provided, they can be arranged in the vicinity of any of the electrical equipment of the vehicle due to their compact structure, thus minimizing the arrangement of power line wires in the car body.