It is possible to splice a new wire into an existing electrical system, and it is a fairly easy process. It is important that all safety steps be taken to protect from any electrical discharge during this process.
Start by turning off the electricity to the working area using the breaker and then test the wires with a voltage tester to insure that there is no power. Then, strip 1 inch of the covering off of both the new wire that is being put in and the existing wire that will be spliced into. After twisting the bare ends of the wires together, cut the bundled wires down to a 1/2 inch, and then secure them with a wire nut.