Equip a drill with a 1¼-inch paddle bit. Drill a hole through the ceiling, working from the attic, between the studs on either side of the electrical outlet nearest the porch roof. Drill a second hole through the exterior wall into the inside of the porch roof.
Drill a 1¼-inch hole through the underside of the porch roof where you will install the lighting fixture or electrical outlet.
Tie one end of a string to a ½-inch magnet and secure the string with electrical tape. Feed the magnet through the hole in the underside of the porch roof.
Guide the magnet to the hole in the exterior wall by sliding a piece of scrap metal along the underside of the roof to the exterior wall.
Pull the magnet through the exterior wall and feed it through the hole in the ceiling to the electrical outlet.
Turn off the main power supply to your home. Remove the electrical outlet cover with a screwdriver. Wrap one end of the new electrical wire around the string and secure it with electrical tape.
Pull the end of the string extending from the underside of the porch roof to pull the wire through the wall, ceiling, exterior wall and porch roof.