How to Replace a Single Pole Wall Switch
Step 4: Inspect Switch Wiring
Check the terminals on the switch with a voltage tester to make sure the power is off. Examine the switch, noting which wire is attached to which screw. Before disconnecting the wires, flag or label them so you’ll remember which one is which. Since the switch pictured had a black and white wire running through it, the white wire was marked with black electrical tape to indicate it was hot.