The invention provides a washing machine and an assembly method thereof. The washing machine includes a casing, a tub installed within the casing, a cover coupled to the top of the casing and having an opening for introduction of laundry, a control panel attached to the cover to enable selection of a washing mode, and a lower electric component located below the tub, such as a drive device. The washing machine may be manufactured to further include an integrated wire harness having one side coupled to the control panel and the other side coupled to the lower electric component for transmission of an electrical signal, and a guide provided at an upper edge of the casing such that the wire harness is fixed to and extends along the guide. The integrated wire harness may achieve reduction of manufacturing costs and prevent fire of the washing machine due to insulation breakage.