A wire harness assembly and a method of forming such a wire harness assembly is presented. The wire harness assembly includes a plurality of wire cables and a wire support defining elongate slots having open and closed ends. The cables are disposed within the slots. Retaining teeth are defined by side walls of the slots and are configured to separate one wire cable from another wire cable in the same slot. The wire harness assembly also includes a slug formed of a moldable material that encases the wire support. The slug also encases a portion of each of the wire cables. The wire harness assembly further includes a grommet encircling the slug. The slug may be formed by disposing the cables within the slots of the wire support, arranging the wire support and the cables in a mold, injecting a moldable material into the mold, and curing the moldable material.