Available after completing "A New Threat". Once you've installed the Radar Beacon into Ada, she reveals the position of the second radar beacon: near the Nahant Chapel. You'll find a group of robots, kill the leader and you'll find the second beacon.
After a short conversation with Ada, you'll find the third and last beacon at the Fort Hagen Satellite Array.
Inside the Array you fight yourself through robots and Rust Devils until you find Jezebel. Talk to him.
After you both set your "deal", fight Ahab and leave the Array. Once you've talked to Ada and gave Jebezel a new body, and speak to him. The quest is finished afterwards.