Generally electrical circuits are fabricated as PCB(Printed Circuit Board) and mounted on a casing of the product. And it requires lots of other parts and some labor for assembly. Recently a molding technology is increasingly applied to embed simple circuits on a plastic casing. The technology is called as MID(Molded Interconnected Device). By using this technology PCB fabrication can be replaced by molding, and lot of the corresponding assembly process for the PCB can be eliminated when if the circuit is simple enough to molding. Furthermore as the improvement of conductive materials and printing technologies of electric circuit, simple circuits can be printed directly on the part casing. It reduces the complexity of the product design and production cost also. Therefore this paper introduces a new MID fabrication process by using direct 3D printing technology. And applied to an automotive part of cruise control switch. The methodology and design is shown.