Down Under
With the TABO security system disabled, it's time to shutdown the primary security power grid. The tunnel you entered from the North Sentry takes you to an underground security station.
When you exit out into the pad area, that should invoke a fight between the brigade and the snipers
Cross the pad area and step in front of the center column on the other side (a switch is revealed)
Flip the switch, one door is revealed, and after a short while, two more doors and another switch are revealed
Flip the second switch, and after a time delay, the doors will open
A few GATs meet you on the way in, after taking them out go to the left up onto the mezzanine, recharge and flip the switch (an alert is flashing between the two panels)
At the end of the security corridor a stairway is revealed, take that stairway up and flip the light switch on the left (read the terminal, and continue to read this terminal throughout the level and note the status changes as you progress)
Follow the path along the windows until you reach a switch, then flip that switch (avoid shots coming from outside)
Head back downstairs and through either of the passages which lead outside (SPAMs await you)
Avoid the SPAMs and run to the left down some stairs and to a guard station with a switch
Flip the switch, head back upstairs and go down the stairway in the center of the outside area (you may want to recharge and save first, and to save head back out to the pad area and look for the save buffer on the left, and you will have to take out both bike cops to effectively use this save buffer)
At the bottom of the outside stairway, head to the right (down here there are 5 servo switches, snipers, and a lot of darkness)
Find the columns that form a partially enclosed area and use the save buffer there (which means you can avoid the bike cops if you want, I suppose)
Head north and locate the other set of columns, then quickly run through the enclosed area (a set of bars appear, so if you are not quick enough, you're trapped behind the bars)
Now shoot out the bars, and flip the switch on the backside of the column (you'll still want to do this quickly because there is an arrow gun in operation on the opposite column)
There are two other square-ish columns down there, each with a switch on both sides, so locate the one that is now enabled (should be nearly on the other side of the room from where you are now)
Flip that switch, and a switch in the other column is enabled, so flip that switch, back to the other column, flip again, back to the other column, then flip that final switch
Head back up to the outside area, back into the security corridor, up the stairs and this time to the left
Continue on until you reach the two switches (with an alert between them)
Flip both switches, then head back down to the security corridor
Head into the newly revealed room on the right as you come down the stairs, turn the key to activate the power grid disarming switch, then step on the platform in the center
You are teleported to the guard station with the switch, with a new path to a second guard station
Run to the 2nd guard station, grab the SAP card, then right back (you may have to do this in two steps as there are fire demons as well as snipers trying to annoy you, so first take out the snipers out of reach of the fire demons, then go back for the card)
Head back up and return to the security corridor, enter the room with the disarming switch, and use your card to activate the switch
Now head back out to the pad area (if you already took out the bike cops, leisurely save your game and head back over to the tunnel you started in, otherwise run back over trying to avoid the bike cops... you really should kill them you know)
A secret door is now revealed back in that starting area, so take the door up the stairs and onto the roof top
Jump off the roof, then jump down the sewer hole to exit the level (I make it sound so easy)
Eye Candy / Extras
Out in the pad area there is tons of extra ammo on both sides of the entrance to the security corridor
When you flip the first switch in the security corridor, you release the two bike cops in the pad area, so if you want free rein on that save buffer out there, you really need to take out both bike cops
There are two switches in the pad area (next to the save buffer), the first one directly next to the save buffer de-activates the first alarm triggered
The second switch near the pad save buffer de-activates the second alarm and also locks down the power grid control room (preventing the horde of miniature GATs from attacking you, unless you've already met them)
Lots of hightech ammo in the lower area with all the servo switches (but that's not really a secret... in fact, there just isn't a whole lot of secrets in this level)