The ground lines converge at the 1/4" phono jack chassis lead.
The neck pot controls volume and balance. The bridge pot controls bass and treble boost / cut.
Neck pot markings:
(on the circuit board)
BEQ2-BAL (RIGHT)
revB 20150617
(on the pot case)
B504
C504
A504
The pot has 12 pin connectors.
Bridge pot markings:
(on the circuit board)
BEQ3 system - B/T (right)
revC
3EQBBT - CF1 2S 01 20150504
B/T1
VR
(on the pot case)
B103
C103
The pot has 6 pin connectors.
TMB EQ circuit board markings:
BEQ2-BT_MAIN revF 2015-04-10
Click for higher resolution images
You may contact me at kevin@kevinsworkbench.com