When asked by Lieutentant Haggerty the nature of the Courier's visit, one can lie with a Speech check of 30, claiming that their brother is stationed at Helios One, or note that the facility's tower is not working correctly and offer to help fix it with a Science of 30. Also, if the Courier has a reputation with the New California Republic, they can walk inside with little issue.
Talk to Fantastic and Ignacio Rivas and get their passwords to access the mainframe. Rivas will only share his password if convinced that the Courier is working with the interests of the Followers of the Apocalypse. Otherwise, it can be pickpocketed off him.
Use the two reflector control terminals outside to connect to the HELIOS One mainframe.
Distributing power to Freeside and Westside pleases the Followers of the Apocalypse, but won't benefit as many people as it potentially could.
Distributing power to the full region, resulting in people getting the same small amount of energy with frequent brownouts. This option results in fame among the Followers of the Apocalypse, as well as a Big Book of Science, three stimpaks, and two doctor's bags from Ignacio Rivas.
Distributing power to the full region at emergency output levels overloads the plant and results in no fame, but Rivas will hand out the stimpaks and doctor's bags, but not the big Book of Science.
Get outside and initiate reflector retargeting from the console.
Talk to the idiot wearing glasses in the back of the HELIOS One plant building.
Connect to the HELIOS One mainframe from the western reflector control terminal.
Connect to the HELIOS One mainframe from the eastern reflector control terminal.
Restore power to the HELIOS One mainframe via an auxiliary generator.
Use the HELIOS One mainframe to send power to a destination of your choosing.
OPTIONAL: Arm ARCHIMEDES security system to wipe out all nearby NCR soldiers.
Initiate reflector retargeting from the console on the tower observation deck.
Talk to Fantastic.
Talk to Ignacio.
In order to avoid glitches and bugs, it is a very good idea to wait by the Reflector Control Panel at the top of the tower until the entire powering up sequence is done, whether the player has elected to activate Archimedes I or not. The sequence ends with a bright white light filling the screen (if Archimedes I was not activated) or a large laser beam coming down from the sky, causing a massive explosion (if Archimedes I was activated).
If Arcade Gannon is with the player, he will encourage the player to distribute the power over the Freeside and Westside districts of New Vegas, saying the NCR does not need it. With Intelligence 7 the player can convince Arcade that the NCR needs HELIOS One as a backup. Whatever distribution choice the player makes, he will comment on it. Arming Archimedes I will cause him to get angry and leave permanently.
Activating the Archimedes I defense system while having Boone as a companion might cause him to confront the player, and possibly leave or become hostile, depending on the player's current NCR reputation. (This is not special to Helios One; he will confront the player if the player's NCR fame/infamy ratio goes below neutral, or if he's warned the player once about hurting the NCR and their reputation gets worse.)
If the player did not arm Archimedes I during this quest, they can come back later and arm it, then walk outside and the attack sequence will play (if they didn't choose option 5 the power during the quest), producing the same infamy gain as if they did it during the quest. However, the NCR troops inside the building will not disappear, nor Haggerty and her troops at the front entrance, and all NCR troops in the area will turn hostile. Activating Archimedes I will not activate Euclid's C-Finder.
If the player returns after the Legion have taken over (after activating Archimedes I), Ignacio Rivas will be dead and Fantastic will be wearing a Legion uniform. He has a whole new set of dialogue about his belief that Caesar's Legion is the next big thing.
The passwords to the Eastern and Western Reflector Control terminals can be converted from hexadecimal into ASCII, producing the phrases "My voice is my passport." and "Too many secrets". The phrases are originally from the movie Sneakers (1992), starring Robert Redford. They were used as computer passwords in that movie.
A number of remaining resources indicate that at one point this quest included a method for completing it on behalf of the Brotherhood of Steel, allowing them to take over the facility. Among other resources, the quest includes greeting dialogue for Brotherhood guards, indicating their satisfaction at gaining control of HELIOS One. Other unused resources include the guards themselves (FormID 00143924) as well as the corresponding dialogue faction for these guards.
PCPlayStation 3Xbox 360 If Fantastic is killed before the power is restored, Ignacio Rivas may not provide the quest-ending dialogue option after powering up the plant and the quest cannot be completed. If this happens the only way to complete is to kill Ignacio at a loss of Karma, and reputation with the Followers of the Apocalypse.
PCPlayStation 3Xbox 360 If the player leaves the room after activating Python, but before he does the fixes to the generator, he will be deactivated when walking back inside again, and will not perform the fixes.
PCXbox 360 If you obtain the password for the second terminal without talking to Rivas and activate Archimedes II, Rivas will refuse to talk to you afterward and the quest cannot be completed. Alternately, kill Rivas and the quest will complete or fail but no XP or Loot will be given to the Courier.
PC If you are doing the NCR quest chain and go to Hoover Dam to talk to the Colonel Moore before you finish That Lucky Old Sun, Fantastic will be there instead of Helios One, meaning it is impossible to finish if it tells you to talk to Fantastic. Sometimes, it actually seems to work to go to the Hoover Dam and simply kill Fantastic to complete the quest. The guards will not get hostile if this trick works. Unclear however, how this fix affects any further quests.
PC If you fast travel away before the sequence after using the switch on the tower finishes, the end quest dialogue with Ignacio is missing from the speech options. You can still finish the quest by killing him.
PC Sometimes when you go to select your choice of how to distribute power at the mainframe, and you have Gannon in your party, his speech options will not come through. This makes it one unable to retrieve the trust points needed to obtain Gannon's quest.
PC Sometimes the guard dogs guarding one of the terminals may not appear.
Xbox 360 Choosing to disarm the Archimedes defense system after activating it may not work; the sequence may play anyway.