I purchased a complete set of wires and harnesses for my truck restoration from Tyree and had excellent service and the wires are perfect. There are two reasons I am satisfied. First, I have all of the Ford archives drawings for my wire harnesses and I verified they were correct BEFORE I ordered anything. I was armed with correct wire sizes, colors, loom colors, etc. For most of the common harnesses, like the headlights and instruments, it was easy to pick out a correct harness. For my truck specific harnesses, like the rear tail light, I worked with Tyree to make sure each harness was correctly manufactured according to my (Ford) specifications. These turned out perfectly with the right wire colors, lengths and importantly for me, the correct loom color trace (red thread). I used the same process for unique harnesses like the optional rear right-hand tail light cross-over harness, something that most people have no idea about. As others have mentioned, if you aren't able to be very specific to what you want and what will make you happy, the chance of being disappointed is high. If you leave decisions to someone making your wires in the dark, it's no wonder that there will be problems. Also, I had the experience of finding out that the harness everyone thinks is the correct one, is actually not so. I had to insist on having wires made my way, not some universal fit which never fits right.
Sorry for the long tale. I only have ordered one harness from Tyree and there are others who will make harnesses just as well. I'm lucky to live abouta 2 hour drive from Tyree, so I was able to visit his shop and take time to explain what I wanted in person, something not everyone can do and a far cry from ordering through a keyboard. I found Tyree to be very flexible with my very specific and demanding order. One harness didn't meet my expectations and he took it back and exchanged it for one I was satisfied with - no charge.
I respect DavidG completely, and bow to his expertise. knowledge and advice. I'm sure his experience is valid, I'm just adding my experience and circumstances to the discussion. If you want a custom harness, I suggest that you provide a complete drawing of any harness with all of the material specification, lengths, fasteners, etc. so the builder can make what you want the first time.