How to Wire a 120-Volt Wall Outlet | Home Guides | SF Gate Turn off the breaker that supplies power to the outlet you'll be changing. If you do not know which Test the wall outlet for power with a voltage tester. These are available at hardware stores. They Remove the cover plate on the outlet to be wired. In most cases you will need a small slotted-head Test the wires on the sides of the wall outlet. This is a precautionary test in case the socket is See all full list on homeguideste 120v Wall Outlet Wiring | Home Guides | SF Gate Outlets have an extra terminal pair that allows you to branch off the circuit to another device, so when you wire a 120-volt outlet, there may be two cables in the box. 1.