A wire installation tool for installing a wire through an existing wiring harness includes a handle configured to be manually grasped by a user, an elongated shaft extending from the handle, and a wire engagement feature disposed at the free end of the shaft. In one aspect, the wire engagement feature is a generally flat elongated plate defining two openings sized to snugly receive the wire and spaced apart a distance sufficient to receive the wire bent to a curvature between the openings. In another aspect, the wire engagement feature includes a pig-tail element about which the wire is wound and held by friction between the wire and the pig-tail element to hold the wire in engagement with the wire installation tool as the tool and wire are pulled through an existing wiring harness.