After having helped Fatin and Tolga during "The Great Train Robbery", Fatin will contact Crane again and ask for his help. Go to the brothers, who are located in the far southern portion of the map, along the train tracks.
Upon arriving at the carriage, knock on the carriage door and speak to the brothers. They will give a list of items they need and offer the Geiger device. Take it from a nearby crate and return to the brothers after obtaining the items.
The brothers will state that they need some time, but eventually they will contact Crane again and ask for some fuel. They recommend going to the wall, as many vehicles are parked there. Return to the brothers with the fuel after obtaining it to finish the quest.
