A wire connection structure for vehicle optional part includes a power socket connected to a vehicle power supply, and obtains a power supply for an optional part by cutting in a feeder path supplying electric power to the power socket. In the wire connection structure, a main-side output cord branched from a main harness is preliminarily connected to the back surface side of the power socket by way of couplers. In addition, each optional part harness is provided at an end portion thereof with an option-side output cord and an input cord, which each have a standardized structure. At the time of additionally installing each optional part, the option-side output cord is connected to the power socket, and the main-side output cord or the option-side output cord, which has been detached from the power socket, is bent into a U shape and connected to the input cord.