A method for manufacturing a wire harness includes: disposing a trunk harness, a branch harness and control boxes on a workbench and attaching the trunk harness and the branch harness to the control boxes; connecting the control boxes to an external device via the branch harness; and switching operation mode of at least one of the control boxes to an information writing mode for inputting information for operating the electric component to be connected to the branch harness into the at least one of the control boxes and then inputting the information from the external device into the at least one of the control boxes via the branch harness.