Step 11: Shielding and wiring
--Remove the existing wiring, knobs, etc. Be sure to save all the parts.
--Cover the backside of the pickguard with foil. Use spray-mount glue, and heavy-duty aluminum or copper foil.
--Same with the routed cavities of the guitar body. Spray-mount could work here, but rubber cement is easier to control. The bridge/string ground can be attached directly to the foil with a screw--so it won't need to be desoldered every time the pickguard is removed.
--Separate the shield ground from the main ground. Connect to main ground at only one point (to remove any ground loops.)
Here's a great link describing shielding in detail: www.guitarnuts.com . This includes wiring for standard 'Strat' 3-pickup setup, and was my reference. Be sure to pay special attention to the sections on electric shock!
Take several photos of the existing wiring BEFORE beginning. If you screw it up, you can always start from scratch.
One tip: once the wiring is done, tidy up the jumble with those little plastic zipties. Not only makes it less confusing, but seems to help the noise ratio (maybe my imagination; or could it work like a 'twisted pair' cable?)
Every guitar has a different wiring schema, so best not go into detail on actual connections. Here are a couple links with wiring options:
Acme Guitar Works
Craig's Guitartech Wiring
GuitarElectronics Strat diagrams