One question about the 4-way switch- does the earth from the neck cover have to be specially grounded? A guide I found mentioned this but I don't get where it's coming from.
When you add a switch to put two single-coil pickups in series, the "ground" wire from one pickup is no longer grounding the end of the coil, instead it's "adding" that pickup to the second pickup. This doesn't cause any problems with uncovered pickups (like Strat pickups).
However, on a regular Tele neck pickup the ground wire is grounding both the pickup coil
and the metal cover. So in series mode, the cover would no longer be grounded - it becomes part of the live circuit. Result - a lot of hum.
Therefore the cover needs its own separate, permanent ground wire, soldered to the back of a pot. It's basically doing exactly the same job as the bare fifth wire in a 4-conductor humbucker cable.
