adding a new electrical outlet to an existing run is a straightforward process here's how to do it turn the power off at the circuit panel and test the existing outlet to ensure it's off then remove the receptacle and detach the wires install the box for the new outlet remove the incoming wires from the old box and run them into the new one then cut a new length of the same gage cable to run between the new outlet and the old and insert the cable into each box to wire the new box splice the wires from the new cable onto the old along with pigtails that will connect to the new device once connected fasten the receptacle and repeat the splicing process in the old box to finish turn the breaker on and test both outlets to make sure everything is wired correctly you