This paper presents a standardization method for designing wire harness systems, based on the control types and functional blocks, for use in commercial vehicles. With a rapid increase in the installation of systems with added new features, it is very important to develop a reliable wire harness design in a short time by standardizing wire harness designs and reusing the standard design. Because the function of a system, particularly, for commercial vehicles, varies significantly on the basis of the requirements, regulations, and options, it is not effective to establish one standard design for one system. In addition, a system with the same function may differ in terms of the input conditions and output loads on the basis of the installed vehicle types, and it is not practical to standardize a harness design targeting an entire system. In this study, the wire harness designs of a system were classified into six categories based on the control types of the system: switch driven, control of a switch, control of an electronic control unit, unit driven, control of a unit, and connector operation. Then, a wire harness design of each system was divided into three blocks according to their functions: the control, drive, and monitoring blocks. The standard wire harness designs were made for each functional block of each control type. The advantage of this proposed method is that an effective and practical design can be obtained, which covers the diversities in the same system for different grades of commercial vehicles with a reduction in the number of wire harness supplements.