First use the comm terminal and the pattern buffer. Flip switch 1, then quickly run for door A. Enter the long corridor to the south. (If you like, you can turn on the lights with the switch to the east.) Ride down the large elevator at the end of the corridor, then head to the room with the three walls in the center. From there go through the door to the south and up the stairway. The door to the room with the comm terminal ahead of you opens almost as soon as you enter the south corridor (beware of ambushes coming from here, and do remember to check the terminal). Near the end of the south corridor, you'll find switch 2, hidden behind a metal panel. Flip it to open door B, allowing access to a 2x recharger and pattern buffer.
Turn around and head west, then turn left at platform C, which isn't active yet. Behind the first door on your right there is a staircase which will take you to the end of the corridor here. Head on until you reach a room with 4 repair switches, a comm terminal and also switch 3. Flip everything, and retrace your steps until you come to platform C, which is now active. It will take you into a series of service corridors, where you must first find switch 4. Take the first left and grenade-jump up to the higher ledge (there are some grenades nearby if you need any), turn right at the end to find switch 4 (opens door D). When you have found and flipped it, head back and drop down into the lowest corridors, turn right at the end to reach the circular room where you'll find switch 5. Flip it to open the wall behind you (door E) and destroy the circuit panel there (switch 6). This opens door F into the last room.
Head back into the service corridors and work your way through the
remainder of the lower corridor until you return to the main complex.
You'll need to flip switch 3 again to reactivate platform
C before re-entering the service ducts. Follow the upper corridor
to the final room. Destroy the two circuit panels there. Finally,
activate the comm terminal to teleport to the next level, Big