If not youll have to wire a longer wire from the light fixture to the switch or from the switch to the power source. Install the new light fixture and fish the wires down to the switch box.
Adding Light Switch To An Existing Circuit Home Improvement
How to add a light switch to an existing outlet. From the switch new 2 wire cable is run to the new light location. Disconnect the wiring from the light fixture and outlet. The neutral for the new light is taken from the receptacle and spliced to the new white wire and to a pigtail that connects back to the receptacle. Wire must then be fed through the hole across the space and into the wall with the switch. After identifying the line and load terminals on the switch remove the wire going to the light fixture twist it together with the wire going to the outlet add a jumper wire cap them and attach the jumper wire back to the switchs load terminal. Holes must be drilled inside the stud bay either through the floor into the crawl space or through the top plate into the attic at both the existing outlet and the new switch.
You then splice all the white wires and all the ground wires in the switch box together. If your wiring is long enough you can use it to run to the switch. Hook up the outlet as you normally would. Twist and cap the white wires connect all the ground wires to the ground screw and youre done. To add an outlet to a light switch you start by making a pigtail using the hot wire the wire going to the fixture controlled by the switch and a third length of wire. The switch comes first in the new part of the circuit and new 2 wire cable is run to it from the outlet.
Wire must be run from the outlet to the new switch and that isnt always easy.