Hello and welcome.
disclaimer - I'm not an expert on wiring - so take this as my best guess.
So the Vcc on the middle pot (the tab on the left that has the red and yellow wires soldered into it) should have one going to the middle tab on the 1M pot, and the other going to the pickup selector.
The red and white wires (the coil tap) are run through the switch. This is a DPDT switch so the two switches are the two sets of three pins (6 in all) on below the Pot. For sake of convenience lets say the left three pins represent from top to bottom A1-PoleA-A2 and the right three pins B1-PoleB-B2.
When you pull up up the pot, it completes the circuits betweeen A1 to and the Pole, and also between B1 and the Pole. It also opens the circuits betwen the Pole and A2 and the Pole and B2.
In this case, since the only switch of the four (A1-PoleA-A, PoleA-A2, B1-PoleB, and PoleB-B2) that is wired is B1-PoleB. PoleA and PoleB are wired together in the diagram and attached to the chassis of the pot which is ground (they could have been attached to the third tab of the pot (the one on the right), since that is also ground.
B1 is soldered to the red and white leads from the humbucker and PoleB is soldered to ground, so s
when the pot is pulled up, the coil should be tapped.
The middle pot is the treble cut (low pass filter). Since nothing is on the middle tab (the wiper arm) the turning the knob shouldn't do anything - the circuit stays open (meaning nothing happens when you turn it regardless of whether it is up or down.
My understanding is there should be a cap from the middle tab to ground (either the right most tab, or the chassis). 0.022 microFarad that's likely why the blob of solder is there.
OzarkTim wrote:The previous owner said the humbucker was split when the pickup selector is in the 4th position, didn't mention the push/pull (probably didn't want me to pull on it and have it just come right out) and said the two tones were treble and bass.
Without seeing the circuit photo - it's hard to say. consult this diagram:
Legacy HB wiring diagram (2001-2012)
Good luck!