“This gadget I'm handing you is called an override module! Mr. House had two of these made years and years ago - just like him to think ahead! Take the module to the El Dorado substation and attach it to the power control terminal! I'll handle the rest!”— Yes Man
In order to control Securitrons beyond the confines of the New Vegas Strip, Yes Man requires the Courier to install an override module in the vicinity of Hoover Dam. Additionally, President Kimball must be kept alive so he can take the blame for the defeat of the NCR at Hoover Dam, absolving New Vegas.
The Courier will be given this quest once they have finished all previous Wild Card quests from Yes Man. It requires the player character to upload an override chip into the El Dorado substation controlled by the NCR. An optional objective to the quest is for the player character to save President Kimball when he arrives to give his speech. This option is only available if the player character's reputation with the NCR is in good standing, otherwise, the quest cannot be accepted from Yes Man.
The main part of this mission is very simple. Go to the El Dorado substation and upload the override chip into the terminal located inside. There will also be a few NCR troops inside though that will shoot on sight so try to sneak in with a Stealth Boy if possible. The best way is to wear NCR armor, the guards don't attack the player character that way. If the optional part of this quest is done and the Courier kills the troops in the substationm, it will have little impact on their reputation because the player character is well-liked. Another way to avoid being attacked by the NCR troops in the substation is to immediately exit it once it has been entered. When the player character then enters it a second time, the NCR troops will not attack them.
Optional: Yes Man asks the Courier to convince the Followers of the Apocalypse to give full assistance to the New Vegas region; simply go and talk to Julie Farkas. Unless they are idolized by the Followers, she will decline the Courier's request, mentioning a short supply and limited resources. One can obtain idolized status by donating medical supplies, leaving and returning to repeat the cycle until given idolized status and offered to join the Followers. Once this is done, report back to the Lucky 38 and complete the quest. Note: Due to a scripting error, this optional objective will only become available after one has completed Friend of the Followers.
Unless one is wearing NCR faction armor and so act in disguise, Boone will leave the Courier if he is with them when installing the override chip at the substation. Without the benefit of a faction disguise, a work-around is to tell Boone to wait outside of the substation so that he does not witness the chip installation, then he will remain with the Courier.
If Boone's quest is done beforehand, he doesn't seem to leave as long as the player character doesn't kill anyone.
Even if the player character is Idolized with the NCR, they will lose the quest You'll Know It When It Happens if one goes to the El Dorado substation first. Completing You'll Know When It Happens first and then going to the substation results in the quest ending with the player character's NCR fame at 'neutral' or higher.
Doing the optional quest of asking Julie Farkas to support an independent New Vegas has no effect on the Old Mormon Fort ending, although the Followers will leave Medical supply boxes for the Battle of Hoover Dam.
A cut stage of the quest required the player character to meet a Securitron near the El Dorado Substation after planting the override chip. The Securitron would lead them to a nearby ridge facing New Vegas, and a cutscene would activate showing the Lucky 38 being lit up.