Harold seems to be having trouble keeping hold of his body parts. The player can find him in the first section of Los where the trader is. Harold asks the player to find three of his missing pieces in exchange for a small reward. The parts are scattered throughout the rest of Los along your quest:
As you head through Bridge East you come to a crater where your only means of travel will be hopping across pipes. If you head west on the pipes you will eventually find a ripper. From there, head east until the road ends again. There is a short path to the southeast which will lead you to a footlocker containing Harold's eyeball.
The next piece is in the Docks Shipyard. You'll start by heading southeast through there and once you hit a save point you'll start heading southwest before rounding a corner and heading north. Eventually you'll find a small path off to the side where you'll find an irate ghoul that likes to throw radioactive goo. Killing him will net you Harold's arm.
Finally, the last piece of Harold is in Docks Warehouse area. Eventually you'll come to a sort of church and a button with a sign that tells you not to push it. Push it anyway and head through. There's an alley to the east wherein you can find Harold's Toe.
Return all pieces to Harold to receive the reward. Don't hesitate to do this because once you progress through the area you cannot come back.