An electrical junction system for automotive internal wiring has a wiring board provided with branching conductors formed by a multiplicity of bus bars on an insulation plate, the branching conductors being adapted to be connected to electric wires in a wiring harness to form branching electric circuits. The electrical junction system has a printed circuit board detachably mounted on the wiring board, the printed circuit board generally or inclusively carrying a plurality of circuits incorporating a multiplicity of function parts which are used semi-permanentally such as relays and associated control elements.