An electrical double light switch is nothing more than two single-pole light switches stacked on top of each other and molded into one single device. Installing an electrical double light switch allows you to add additional light fixtures without the trouble of cutting a hole in your wall to add a larger switch box. Installing this device will save you time, effort and money by allowing you to wire what are really two switches in the same space where one switch was originally installed.
Turn the electrical power off to the circuit on which you are installing the double light switch by turning off the breaker in the main electrical panel.
Locate the power supply wire in the electrical switch box. The black power supply wire connects directly back to the breaker panel and feeds electricity to the switch.
Locate the two black wires inside the switch box that connect to the light fixtures. There will be a total of three loose black wires inside the switch box.
Wire the light fixture side of the electrical double light switch. A double light switch is a single device with one switch stacked on top of the other. Wrap one of the black light fixture wires to one of the two screws on the left side of the double light switch and tighten the screw. Wrap the other black light fixture wire to the remaining screw on the on the left side of the switch and tighten it as well.
Connect the black power supply wire to the electrical double light switch. Use wire cutter/strippers to cut a 4 inch piece of 14 gauge THHN solid black wire and strip 1/2 inch of insulation off of each end—this will be your jumper wire. Attach the jumper wire to both of the screws located on the right side of the switch by wrapping the stripped ends around each screw. The jumper wire allows electricity to flow to both switches. Connect the black power supply wire to one of the two screws (one screw will hold two wires) and tighten both screws.
Install the electrical double light switch into the electrical switch box. Push the wires into the electrical box and attach the switch to the bottom and top of box with the screw provided with the double light switch.
Cover the double light switch and the electrical switch box with a duplex receptacle cover plate.
Turn the electrical power on to the circuit you installed the double light switch on by turning on the breaker in the main electrical panel.