I don't have a schematic, but I know that the three knobs on the lower bout are individual volume controls and the single knob on the upper section is a master tone.
I would imagine each of the three pickups is wired directly to its respective volume pot and then to the tone pot/output jack. I'd guess that the pickup is wired to the center lug of the volume pot (like a Gretsch). This prevents the "if you turn one pickup off, you turn them all off" thing that happens in the middle position of a Les Paul-style wiring. Wiring the tone pot to the output of the volume was typical of Gibson in that era.
Also worth noting that at least one pickup was typically out of phase. It seems to vary example-to-example, but I've heard that it was usually the middle or bridge pickup.
EDITED TO ADD: I just found the attached schematic on Google. Looks like I was correct on all counts.