This diagram and video demonstrates how to wire you pickups for series/parallel switching in a Les Paul, using push pull tone controls.
Most pickups are wired in series, its what gives it it's full and beefy sound. Putting the pickups in parallel, gives a single coil-ish tone but with a noticeable loss in output, resulting in a very thin sound.
Note - this wiring diagram is colour coded for House of Tone or Seymour Duncan pickups.
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