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How to wire a double switch
Cut the power to the room you're working in.
Head to your circuit breaker and turn off the flow of electricity in the room you are working. Usually the correct circuit is labeled, but if it is not you should turn off all the power in order to be safe.
The energy going to a switch is nothing to scoff at, and it can cause serious damage if you come in contact with it. You should still wear gloves and grounded, rubber soled shoes in order to be safe while working.