Originally Posted by
Simon Barden
Always best to build most of your wiring harness out of the guitar on a piece of cardboard. I use a piece of paper to mark out the potentiometer holes on the top of the guitar, transfer that to a piece of cardboard and poke holes through. Then fit the pots through from the underside (otherwise it won't work as well). Using coloured pens, you can draw the circuit/wiring on the cardboard, to make it easier to not get your wires crossed or connected to the wrong lug on a potentiometer.
Then you can work on fitting the wiring between pots (and depending on the style of guitar, sometimes the selector switch and output jack as well), when you have a lot of space to do so, and not when they are in the bottom of the control cavity. You can then cut wires to the correct length, without having excess wire everywhere - never good for tidiness nor noise pickup.
With everything out of the guitar, you can more easily test the connections with a multimeter to ensure they are made well, so that if there are any problems later, you should be able to discount the wiring of the bits you've already tested.