Install a junction box by attaching the box to the studs or ceiling joist with screws, knocking out the plugs, installing cable clamps, pulling the wires into the box and making the splice. Attach the cover to the box. Electrical codes require all wire splices take place in a junction box for greater safety. Turn off the power before beginning the installation process.
Once the power is off, use an electrical tester, and test the circuit. For your own safety, do not proceed if it is energized. Disconnect the old splice, and feed them into the new junction box. Use lineman's pliers to twist the wires together and an appropriate wire nut to complete the connection.
Installing a junction box is the proper way of extending a circuit and adding more outlets. Before adding new outlets, check to see if the circuit has the required capacity. Adding more outlets to an already overloaded circuit makes the existing problem worse. If the circuit is overloaded, reduce the load by installing a new circuit and circuit breaker.
Electrical splices produce heat due to an increase in resistance. The junction box contains the heat to reduce the risk of fire. Although codes require them, owners of older homes often find wire splices made outside of junction boxes.