Introduction:
The reality with wiring is that it looks simple and easy, and you may have wired up some kind of circuit yourself that worked out fine, but there are methods and techniques for wiring in general, and especially in special applications, audio in this case, one has to know and understand in order to get the best performance, avoid failure, and with that prevent the need for future repairs. And since we are speaking of audio here, we want to get a preferred sound and suppress noise too, so circuit design is also important, and more difficult than the wiring part. I have had customers bring in guitars they wired themselves that were well done, but more often than not they are only partially well done or not at all. Heres a common DIY mistake:
Twisting two wires together have no mechanical bond, and electrical tape although a good insulator, doesn't last, and is not a permanent solution, and in this case it was a source of an annoying crackling noise.
The way the switch is wired below has just about every mistake one can make. Everything from too much exposed wire to bad mechanical connections, where some wires don't even touch the contacts directly but rather sit on a blob of solder that was not up to the right temperature to flow and make a good connection. Add to that, the person who did the wiring did not understand the diagram he got the desired custom pickup configurations from, and it didn't work right in some positions and not at all in others. I was told "My little brother did it" when I pointed out the mistakes.
Although not the wiring itself, heres something to be aware of:
This is what can happen if you use knobs made for solid potentiometer shafts on pots with split shafts. It can be done though, it just needs a good workaround.
Many OEM's making guitars think guitar circuitry is simple too, and without ever employing an actual electronics engineer to design circuits that could be much better, they just follow what others have done before them who didn't have a specialist either and therefore copy others mistakes. They have created a tradition many people see as gospel, it is not, and a 300 or 450 ohm pot is not a crime... I went to school to become an electrician, studied engineering, and have worked in the industry including making circuitry for research and development equipment like spectrometers, microwave assisted chemistry, and other wave technologies. You will be hard pressed to find a better place than 
Lutherie to have work done to the electronics of your instrument.