Head west from the fountain, following your Pip-Boy marker, and make your way through Puesta del Sol to the Switching Station.
Once inside, approaching the locked interior door around the corner will cause Christine to direct you to the fuse box on the wall near the entrance. You must use this to restore power to the station and open the door blocking your way. (The fuse box will also power up the nearby computer terminals in the same room).
You can repair the fuse box with a Repair of 60 (there is a Fixin' Things on the large box to the left of the locked door), or use 3 of the Electric Box Fuses found in various locations in the Puesta del Sol area.
There is a fuse in the same room, in a toolbox near the computers to the right of the locked door.
Exit the station and go right, into the cloud. There is a fuse in a toolbox on the floor.
Also from the station exit, turn left instead and go down the wide stairs, turn left under the archway and keep going left until you are able to turn right. You should see a well-lit opening into a building. Enter and proceed to the top floor. Make your way out to a balcony, where there is a toolbox containing a fuse.
Once the door is unlocked, make your way through the station, dealing with the radio speakers you find along the way. Check the walls for graffiti pointing out some of their locations. Christine's Signal Interference perk gives you plenty of time to destroy them or run past.
There is one speaker to the right of the door as you go through, partially hidden behind the pipes. Another is high on the right-hand wall of the alcove you pass, to your right, in the same corridor. There is a third speaker around the corner and down the stairs, well hidden under the pipes high on the left-hand wall. All three can be destroyed with weapons, but not otherwise deactivated.
Enter the main station area and turn right, following the walkway. Christine will draw attention to the cloud below you. Your destination is across the broken walkway to your left. Below you is a large pipe which can be jumped on and run across to the other side of the room. You can then jump to the base of the staircase and go up, thereby avoiding most of the cloud.
To your right the walkway leads to a Dean's Electronics. It is protected by a shielded speaker, but Christine's Signal Interference perk will once again give you enough time to run around the walkway and reach the terminal to deactivate the speaker. Watch out for the tripwire just in front of the terminal; you can disarm it quickly, or carefully access the speaker terminal and then deal with the trap. Note that the tripwire may already be disabled (or have gone off, possibly moving the Dean's Electronics book) when you enter the building.
Following the walkway left from the top of the staircase leads to a door into a room with a large computer on the left-hand wall, and a terminal in the opposite far corner containing messages related to the History's Sake challenge. Go through the door next to the first aid box on the wall and enter the next room.
Here Christine will draw your attention to the ventilation control system terminal on the wall in front of you. Activating this will clear the poison cloud from lower levels of the switching station and from some areas outside in Puesta del Sol. Along one wall in this room is a fridge and a row of lockers, including Ennis's locker which contains the Remote maintenance terminal password. The lock can be picked with Lockpick 100, or opened with a key which is found in one of the rooms ahead.
With the cloud vented, you can go back down the stairs and safely explore the previous room for a few spare Sierra Madre Chips and a skill magazine, some ammunition near the middle of the room, two stimpaks atop the two big metal boxes next to the ammunition, and a toolbox. A corpse can be found behind a fallen piece of walkway (below the entrance walkway), wearing a Dead Money jumpsuit and carrying the See you in hell asshole note. Watch out for several bear traps under the large pipe you crossed earlier.
Opening the door next to the ventilation control terminal reveals another walkway. There is a security turret to your right at the end of the walkway, and a shielded speaker on the wall to your left. The turret can be targeted and destroyed from inside the room you are still in, safely out of range of the speaker, or deactivated at a nearby terminal, directions to which are noted below (although this requires avoiding detection by the turret while moving quickly enough to escape the speaker and jump over gaps in the catwalk). Directly across from you is a locked door (Lockpick 75), behind which is the terminal to shut down the speaker. To reach the terminal without picking the lock you can instead run down the stairs, take the first right then jump across the gap ahead of you. Then go left up the stairs, jump the gap and go left again, looping around into the room behind the locked door (the door can be unlocked from this side via a wall terminal next to it).
With the speaker deactivated you can safely return to the walkway. Again going from the ventilation control terminal, going down the stairs and taking the first right but then jumping the gap and going straight ahead towards the gray machinery will lead you to a Chinese Army: Special Ops Training Manual (follow the left-hand catwalk around the machinery).
Alternatively, turning right again before jumping the gap to the machinery, then going down the stairs and left over the pipe will lead you to the aforementioned turret control system terminal, which requires a Science of 75 to access. Continuing along this path will take you to your destination at the elevator.
From the room with the speaker terminal, take the door to the right of the terminal and follow the walkway south to the main computer room. (Note, you can also reach the Chinese Army: Special Ops Training Manual mentioned above by jumping across to the right from this walkway).
In the computer room there is a desk to your left with a terminal containing a note about Ennis's locker key. The key itself on the desk. Turning right at this terminal will lead you to your destination in the next room.
Ahead of you is the maintenance elevator on your left. Across from it is the remote maintenance terminal. Christine will approach you and initiate a conversation, expressing her fear and unwillingness to enter the elevator. With various dialogue options you can deduce that she is remembering her experiences trapped in the medical clinic auto-doc, and is showing signs of claustrophobia (and possibly post-traumatic stress).
Your choice at this point will affect Christine's actions later in the game.
You can choose to lie to Christine and trick her into the elevator. This will complete the quest, but you will be unable to use the elevator to quickly exit the station. You will also lose Karma for lying to her.
You can also use the Terrifying Presence perk to scare her into the elevator, and you will still be able to use it to escape quickly.
You can tell her you will look for another way to access the station controls.
Note that you can exit the dialogue without deciding, and talking to Christine again will still give you both the "good" and "bad" options.
You can now search the area more thoroughly. Opposite the maintenance terminal and to the right of the elevator is the vending machine code for the Holorifle reinf. components, lying on top of a computer. Accessing the elevator and going down will give you a written on-screen description of a tiny cramped room full of whirring machinery, exactly as Christine feared. Going up in the elevator leads to an exit back to Puesta del Sol - an upper floor room overlooking the street. Here there is a Fixin' Things on a desk to your left, an absinthe behind a pipe above you, and random items in the containers.
To help Christine you must gain access to the remote maintenance terminal. You can hack it with a Science of 100, or use the Remote maintenance terminal password found in Ennis's locker.
Talk to Christine again and tell her the terminal is usable. She will express her gratuitude and offer her hand in friendship. Once the dialogue ends she will take her seat at the terminal and the quest will be completed.
pc Sometimes, even when you hit "Ventilation Control" on the terminal that removes the cloud in the station, the Cloud does not go away. [verified]
pc If you hack the computer to the maintenance tunnels to help Christine when she is not in your party, You will not be able to help her, and end up having to shove her in the elevator. [verification needed]