The wire from the rear diaphragm, goes through that little hole (between the 6-pin header and the 1G resistor, in the Side B view), and solders to the bottom of that white insulator (to which the middle leg of the pattern selector goes).
The wire from the front diaphragm goes through the little hole next to the JFET, and solders to the bottom of the white insulated pin between the pin header and the pad switch.
The backplate wire goes to that lone hole/pad right in the middle of the board, with a little solder blob sticking out of it, in-between the pad & high-pass filter switch, right next to the padding cap.