How to Hook Up a Switch at the Top & Bottom of Stairs

Determine the locations of the two switches and install an electrical box at each location. This will require cutting a hole in the drywall at each location with a drywall saw. The hole must be large enough to allow you to nail the box to a wall stud. Repair the holes after the electrical connections are done.

Install an electrical box for the light fixture in the ceiling, if there isn't one already. This procedure also involves cutting a hole in the drywall, but if you have access to the ceiling joists from the attic, you only need to make the hole large enough to accommodate the box. You can nail it to a rafter from behind the ceiling.

Feed the cable that connects to the live circuit into one of the switch boxes. Use 3-strand cable, with one hot wire, one neutral and a ground. If you are drawing power from another device, like an outlet, use the same gauge cable as the one already connected to the outlet. Be sure the power is off to the live cable before continuing.

Run a length of 3-strand cable between the light and the second switch box, using cable of the same gauge as the live circuit cable. Pull the ends through the back of the light fixture box and the back of the switch box.

Connect the two switch boxes by running a length of 4-strand cable between them. The cable has an extra hot wire, which is covered with red insulation, and it should be the same gauge as the cables you have already installed. Pull the ends through the backs of the switch boxes.

Strip 4 to 6 inches of sheathing from the end of each cable in each electrical box with a utility knife. Separate the wires and expose the ends of the insulated ones by stripping off 1/2 inch of insulation with a wire stripper.

Install a 3-way switch in the electrical box that contains the live circuit wire. Attach the live wire to the bottom brass terminal on the side of the switch that has two terminals by unscrewing the terminal screw with a screwdriver, wrapping the wire around the screw, and tightening it. Attach the black wire going to the other switch to the top terminal in the same way. Connect the red wire to the common terminal, which is the single one on the other side of the switch.

Twist the white wires together with pliers and screw on a wire cap to hold them together. Twist together the ground wires, which are bare, and attach them to the green terminal on the switch.

Install a second 3-way switch in the other switch box. Connect the black wire coming from the first switch to the top of the paired set of terminals and the black wire going to the light to the bottom. Connect the red wire to the common terminal. Twist the white wires together, cap them, and connect the ground wires to the green terminal.

Wire the light fixture by twisting the black wire from the fixture together with the black wire coming from the switch and screwing on a wire cap. Connect the white wires together in the same way, as well as the ground wires.