In Mission 13: Going Dark, you can use the power switches on the walls of the following four buildings to turn off the lights and get the “Lights Out” achievement.
1. Objective: Find a way into Barkov’s Estate – After passing by the first group of enemies, Captain Price will point out a breaker box to you automatically (outside the first building you enter).
2. Objective: Find Hadir – It is behind the Pool House (main objective).
3. Objective: Find Hadir – It is to the front left of the Clocktower (main objective).
4. Objective: Find Hadir – It is to the front right of the Church (main objective).