The best quality harnesses I have seen come from Rhode Island Wire but most of them likely come from Bauer Electronics. If sources make up their own then the wire & possibly terminals likely comes from those and a few other sources. A lot of the terminal ends are crimped and soldered to prevent warranty problems. The light switch round terminal block is another item to check and be sure it is one of the good ones. Some are too thick and some have ident issues where the rotating part of the switch rides over the cupped terminals of the block.
Reuse a terminal block if not damaged. Repos may not fit. Haven't actually done this, Sacramento vintage was the likely source of my harnesses, and probably the majority of west coast replacements.