Adding a light fixture to an exterior wall is a fairly straightforward project. In a typical installation, the fixture is controlled by a standard wall switch on the interior side of the wall, and the switch is tied into an existing lighting/receptacle circuit. There are a couple of ways to simplify the project: you can install the switch and fixture along the same stud cavity and use remodel-type, or “old work,” electrical boxes for both devices. These boxes have special tabs for anchoring to the wall surface alone and don’t need to be fastened to the wall framing.
Shut off the power to the circuit(s) in the project area at the home’s service panel (breaker box).
Mark cutout holes for the fixture and switch boxes by holding each box up to the wall in the desired location and tracing around it with a pencil. Drill a starter hole inside the cutout line, then complete the cutout with a drywall saw on the interior side of the wall, and a jigsaw or reciprocating saw on the exterior side.
Feed a fish tape, or a straightened coat hanger, down through the fixture-box hole and out through the hole for the switch box. Hook a length of appropriately rated nonmetallic (NM) electrical cable to the tape and pull the tape and cable back up through to the fixture box, leaving at least 12 inches of extra cable extending from each box.
Route another length of cable from the power source location to the switch box. Potential tie-in options may include a receptacle on the same wall below the new switch, a nearby switch box, or a junction box or nonswitched fixture or device accessible from the attic above or basement below the project wall. You might want to hire an electrician to make the power-source tie-in for you.
Feed the ends of the cables into the integrated cable clamps on the boxes, then fit the boxes into their holes. Turn the mounting screws to engage the anchor tabs, clamping the boxes to the back side of the wall surface.
Strip the sheathing from the cable ends using a cable ripper or utility knife. Trim the cable’s wires so they extend 8 inches from the front of each box, then strip 3/4 inch of insulation from the cable wires, using wire strippers.
Connect the switch to the fixture cable and power-source cable, following the manufacturer’s wiring diagram. Mount the switch to its box and install the cover plate.
Connect the fixture’s wire leads to cable wires as directed by the manufacturer. Mount the fixture to its box, making sure to use any weatherproofing gaskets included with the fixture to prevent moisture and insect infiltration. Restore power to the circuit(s) at the service panel and test the switch and fixture.
All electrical installations must conform to the local building code. Consult your city’s building department for recommendations and applicable code requirements.