Power comes into a switch at my house and the wire is connected to an outlet in my garage. The switch controls both plugs. I want to keep this wiring the same, but add a light out in the garage. Can I add wire to the outlet and connect the light that way? Any diagram/suggestions would be helpful.
If your walls are open this will be easy. Adding a light is legal in my state. With the power off pull the outlet, add a piece of romex and run up to where you want your light switch, have at least 6" of wire at the outlet and the box connect the new wires to the outlet or pigtail the wires connecting the black hot wire to the brass colored screw and the white or silver colored sctee to the white or neutral wire, the grounds should be pig tailed and then connected to the outlet. Take another piece of wire from the new switch box location to the location you want your light, if this will be a plug in type of light wire the outlet the same as the first (color wise but no pigtails are needed) , now to connect the switch, pigtail the grounds and connect a short length of the bare ground to the switch yoke it should be a green screw, tie both white wires together (wire nut or other listed device) last connect one of the black wires to one screw and the other black wire to the other screw ( if other than a standard snap switch/ or an electronic switch the neutral may be needed). Note wiring below 8' is supposed to be covered by 1/2" sheet rock or plywood but I have seen so many garages that the wiring is exposed I usually go with what is there. Conduit can also be used to protect the wire and that can be left exposed legally. If the walls are covered it will be a bit tougher but still can be done, you will need old work boxes. These boxes you cut a hole between studs that just barely allows the box to slide in put the wires in the box slide it in the hole then 2 screws tighten the wings or fins depending on the brand. Now turn the power back on and plug in your light. Note a pigtail is a junction of wires that usually has the conductors tied together with an extra piece of wire to connect directly to the switch or outlet. Hopes this helps.