Outbuildings and sheds are only practical as long as they are convenient to use for their intended purpose. One thing that can relegate sheds to once-yearly visits to clean them out is a lack of convenience features such as lighting. To ensure that all building regulations are met and safety measures are followed, hire a professional electrician to make the connection at your breaker box and install a breaker to control the shed as well as a junction box for the light switch inside the shed, from which the rest of your wiring can be run.
Turn off the breaker to the shed to ensure safety when handling wiring. Remove the cover from the junction box by using a screwdriver to expose the wires. Remove the wire nuts from the ends of the wires. Locate the black, white and uninsulated copper wires.
Cut a piece of three conductor cable long enough to run from the light switch junction up the wall to the underside of the roof peak and out to the centre of the shed. Install a square junction box on the underside of the ridge beam at the centre of the shed. Drive two 4 cm (1 5/8 inch) treated deck screws through the holes in the back of the box into the ridge beam overhead.
Cut the insulation from the ends of the cable, about 7.5 cm (3 inches) from the end. Use a utility knife to cut around the cable slicing and through the insulation. Pull the cut insulation toward the end of the cable to slip it off. Strip the insulation from the ends of the wires with wire strippers. Fit the wire into the correctly sized notch in the strippers and squeeze them shut. Pull the strippers toward the end of the wire to pull the insulation off.
Feed one end of the cable into the light switch junction box. Use nail-in type cable clips to fasten the cable to the frame of the shed. Attach it up the wall from the switch to the ceiling and out to the junction box on the ceiling. Feed the cable through one of the punch outs and into the box.
Attach the black wire from the cable running to the shed to the top screw of a single pole light switch. Wrap the wire around the screw and turn it clockwise to tighten it. Repeat this process connecting the black wire from the cable running to the light junction box to the lower screw.
Match the two white wires and the grounds together and fit them into wire nuts. Twist the wire nuts clockwise to tighten. Fit the wire nuts back into the light switch junction box. Wrap electrical tape around the light switch, covering the screws and the ends of the wires. Fit the switch into the box and install the top and bottom screws through the holes in the top and bottom tabs of the switch, into the threaded pockets at the top and bottom of the junction box. Tighten them with the screwdriver. Place a cover over the switch and install the two screws and tighten them.
Attach both white and black wires to the screw terminals on your light fixture using a similar technique as for the switch. It does not matter which wire attaches to which screw. Attach the bare copper ground to the green screw on the back of the fixture to ground it. Fit the plate of the light fixture onto the front of the junction box and attach it using the screws provided.
Install a light bulb into the fixture and install the glass globe, or any other cover as per the instructions that came with the light fixture. This will vary widely depending on the style and brand of light, but typically requires a set screw to be tightened into the side of the fixture to hold the cover in place. Turn the breaker back on and turn the switch to the "On" position to test the light.