Step out of the elevator and enter the room with a machine to the left and three breakers. You have to activate breakers 1 and 3 to open up the container to the left. Pick up the flashlight from it.
There's only one breaker in this area and it's locked behind a fence. To get to it, you have to crawl through the correct body storage drawer in the Morgue.
Continue to the exit or search for the special rooms below. Ignore the rooms if you already unlocked the achievements tied to them.
Take the elevator down to the last area. After leaving the elevator, follow the straightforward path until you reach a pipe. Go down the pipe to reach the Sewer area.