The term 'Part of a Harness' refers to the components used to attach a horse to a cart or other vehicle. The three crossword solutions for this term are REIN (4 letters), HAME (4 letters), and TRACE (5 letters). A REIN is a strap attached to the bridle of a horse, used to control its movement. A hame is a U-shaped piece of metal or wood that fits around the horse's neck and attaches to the traces, which are straps that connect the harness to the vehicle. Together, these three components make up a part of a harness.