What are series and parallel wiring?
Series and parallel wiring usually refers to two separated but related issues. The most common usage refers to how two coils in a humbucking pick up are connected to each other. With series wiring the individual coils are connected end to end. Current flows first through one coil and then the other. This is the way most humbucking pickups are wired. With parallel wiring the individual coils are connected to each other at both ends and current flows through both coils at the same time. Pickups wired in parallel are brighter sounding and have considerably less output than an identical pickup wired in series.
The terms series and parallel are also used to describe the way in which separate pickups are connected to each other in the guitar by the pick up selector switch. In the vast majority of guitars the pickups are connected to each other in parallel. The same rules apply to pick ups wired in series and parallel as a humbuckers coils wired in series and parallel. Two pickups wired in series will have higher output and a fuller tone.