After dealing with Lev's rebellion and returning to Meg Groberg in the Crater Core, head to Vault 79. Use the given keycode to enter, then meet with Meg, Lucky Lou, Johnny Weston, Gail, and Ra-Ra. Speak to Lou once their conversation is over and all preparations are complete; he will detonate the charges around the vault door to allow entry.
Meg will order Gail, Ra-Ra, and Johnny to enter and deal with the vault's security systems while she and Lou stay outside to watch the flank and ensure no betrayals are attempted. Due to Johnny's high demanded cut of the loot, Meg will ask the Vault Dweller to watch his actions in the vault. After either ignoring her conversation or finishing with her, enter the vault itself. The vault is filled with various robotic enemies, including automated turrets, Protectrons, Mister Gutsies, and Eyebots. After reaching the locked door to the security wing with Johnny and co. and listening to his orders, head to the nearby terminal and collect the Vault 79 facilities management keycard. Use it on the locked door directly across from the main entrance, then head inside and flip the breaker.
Afterwards, enter the security wing, which is filled with a large number of robotic enemies. Gail, Ra-Ra, and Johnny will enter a nearby room which locks after them, and one must defeat all the enemies outside, then speak to them using the intercom outside. Johnny will trigger security subprograms recognizing him as an ex-convict while attempting to hack the system - with lethal force to be used upon further failure - and will ask for whether to proceed hacking or finding a different plan. He can be told to stop, or lied to to proceed; lying to him will result in him being killed by turrets inside the room. Either way, the only other option is to use Gail to fool the biometric scanner - guide her through conversation with AC. He will unlock the following security gate, allowing passage into the atrium. An assaultron and other enemies are in the way. After entering the atrium, defeat the robots which spawn, including a three-star legendary sentry bot that emerges from a separate lift under the pool table, which is given plenty of warning of its arrival by the warning lights on the underside of the table and hisses of steam as the seal is released. Choose whether Ra-Ra should unlock only the next door, or try to unlock more; unlocking more will spawn several waves of Mister Gutsies.
The next area is the dorm hallway; near the end is an optional room off to the side which holds the legendary weapon Slug Buster. Ra-Ra can be asked to open the door to access it, or to move on. Afterwards, she will open the door to the next area.
Talk to AC again through the intercom once in the next section. Finishing this conversation will complete the quest and start the next quest, Secrets Revealed. Completing this quest for the first time unlocks the Go for the Gold achievement/trophy. Also, siding with the Raiders with hitting the Vault awards the fashionable raider outfit to the player character.
After entering the Auxiliary Operations Center, Johnny, Gail, and Ra-Ra will enter a room where the door will close behind them before the player character may enter. Requiring the player character to continue the quest using the intercom. However, the door may be open with an invisible wall preventing access, the intercom not marked as a quest objective. In addition, enemies, such as eyebots, may enter the room and prevent Gail and the others from completing a scripted sequence. Exiting the Vault via the elevator and exiting the game to the main menu, while destroying any robots approaching the group, may fix these issues.