How to Wire Electricity for a Garage Consult a local electrician for exact wire size requirements. Pull the wire to the end of the conduit, using the fishtape. Leave at least 3 feet of extra wire at each end, beyond the actual junction boxes themselves. Strip back the wire sheathing and connect the wires to the junction box in the garage and the main panel box at the house. How to Wire a Finished Garage | Family Handyman Figures A, B and C below show the wiring diagrams to add outlets and a switched outlet for a hanging light. It’s important to make sure all the boxes are grounded. Do this by connecting the new (green) ground wire to the existing ground wire at the first box (see “Ground Metal Boxes and Fixtures,” below).