The quest is activated immediately after completing Mechanical Menace. The Sole Survivor is told by Ada that they need to go to the General Atomics factory. Once there, they have to fight their way through the factory. At the far end of the factory, one will find a Quantum robobrain. Killing and looting it will give one the Mechanist device. The Sole Survivor then gives it to Ada who says it is a satellite tracking device. Ada tells them to install it in her so they can use it to their advantage. To do this, one needs to place Ada in a robot workbench which they must build in one of their settlements (Note: If one already has built a robot workbench, a new one must be constructed). Once it is installed on Ada, she will say that in order to utilize it, they have to kill another robobrain somewhere in the Commonwealth that is using the same signal. Ada tells the Sole Survivor she needs them to bring her two additional beacons to decrypt the encryption on the signal. When she says this, she places the locations of the robobrains onto the map and the quest ends.
Investigate General Atomics Factory
Ada said she saw the Mechanist's robots at the General Atomics Factory. I may be able to find something there to help us discover where the Mechanist is.
Search the Robobrain
While searching General Atomics, I discovered a robobrain. Somehow I need to search this new robot and see if I can find anything that will lead me to the Mechanist.
Speak to Ada
I should ask Ada about the strange device I found on the robobrain.
Build a Robot Workbench
Ada suggested I use a robot workbench to install the radar beacon on her, but first I need to find a workbench to build one.
Speak to Ada
Now that I've built the robot workbench, I should speak to Ada to let her know it's ready.
Install the Radar Beacon
Now that the robot workbench is built, I can use it to install the radar beacon on Ada.
Speak to Ada
I successfully installed the radar beacon on Ada. I should speak to her and find out what she's learned from it.
Searching the robobrain and obtaining the Mechanist device may not complete the "Search the Robobrain" objective. [verified]
You can move forward with the console command setstage DLC01MQ02 2400
You can uninstall Fallout 4 and DLC. Reinstall the main game and all DLC EXCEPT for Automatron. Load your current save, and then manually save the game. Then, proceed to reinstall Automatron. Reload the save file and the Automatron questline will restart from 'Mechanical Menace'. When that is completed, do not accept Ada's offer to follow, this will then prompt the player character to send her to one of their settlements. Do not build a Robot Workbench. After sending Ada off, immediately proceed to 'A New Threat'. The game should be able to register the looting of the Mechanist Device from the Robo-Brain, and open up the next quest. Once this is done, then the player character may have Ada follow them and build a Robot Workbench.
If one has built the Robot workbench prior to obtaining the prompt from Ada, the quest will not proceed until the current workbench is scrapped or stored, then rebuilt or placed again. Ada may be modified in other ways, but until the workbench replacement occurs, there will be no option to install the Special Mod that is the Radar Beacon. [verified]
Attaching the radar beacon to Ada may not complete the "Install Radar Beacon on Ada" objective. [verified]
You can move forward with the console command setstage DLC01MQ02 2900.
Upon first entering General Atomics Factory and begins to engage the robots, if the Sole Survivor exits the building, the Robobrain with the Mechanist device will spawn with the player character outside.
It is possible that upon attempting to install the beacon, one may have limited options on Ada, including no "Special Mods" section, possibly due to damage taken during previous fights not fixing properly. If this occurs, attack Ada and kill her, then repair her with a robot repair kit. This will 'reset' her and allow full modification.