A harness isn't just straps. It's an interface between human and a ton of living horse. Collar presses on shoulders (not neck!). Reins go to the bit. Breeching holds the buggy on downhills.
Making
Harness maker — leather master. Rawhide leather, brass buckles, hand-stitched. One harness — 40-60 hours of work. Cost: $800-1,500. Lasts 20-30 years.
Fitting
Each harness fitted to a specific horse. Like a suit — custom measured. Collar too narrow — horse suffocates. Too wide — chafes shoulders. Right collar — horse pulls 8 hours without tiring.