1) Harness gear 2) Harness parts 3) Harness pieces 4) Parts of a harness 5) Trace holders 
To make a hames of something has something in common with “yoke” (see word 62). Again, it’s a term related to fastening collars to animals. The hames are curved pieces of wood or iron attached to the collar of a draught horse, on which you then attach the traces. Put it on the wrong way and, well, you’ve made a hames of it.