Installing outlet from existing wall switch

The two wires going to the switch should be black and a white with black tape since that wire is only hot after the swicth is thrown. You can run that white wire with black tape to a new outlet but you will need another wire, white neutral from the outlet back to the panel or outher outlet on the circle. You may want to test your wires witha meter since it isn't safe to assume the person before you did the correct install.

There are two sets of wires going into the switch box.Each one has a black,white and ground. The ground wires are twisted together and attached to the metal outlet box. Both blaks coming in are attached to the two screws on the switch. The white wires are twisted together with a wire nut. Can you still help me?

Fortunately, the above answer is one of several here recently that assumes all light switches are wired up using NM and a switch loop. Your switch sounds to me like the alternative way, and you have a pair of wires feeding power to the box, and another pair of wires running to the light. If so, it is just a matter of identifying which pair is which.

To do simple checks like this you do need some tools. A test light, a meter, or a voltage detector might be the best place to start with. I came across the niftiest gadget for trouble shooting, a voltage detector. They work through the insulation of wires. There are several brands. I have a GB Instruments GVD-505A, less than $15 at Home Depot. Touch it to a hot wire, and the end glows red. Find the doodad that lights it on one side, and not the other, and you have the culprit. You do not have to open up housings and expose electrical contacts. You are looking at where your hand is, not where the meter is. Most people are capable of doing repairs and will get it going and not get hurt if they use a little sense. The voltage detector makes it even easier.

With the power on, and the switch off, you can just see which black wire has power with the voltage detector. My voltage detector is adjustable and if I turn it up too high, I get false positive readings. Using a meter, as above, check for 120 volts between the one black wire and ground or the white wires. Once you have identified the hot wire, shut the power off, run a cable from the outlet to the switch box. Connect all the whites, all the grounds, and and the new black to the same screw as the black that wasn't hot. This is best done with a third short black wire connected to the switch and then wire nutted to the other 2. If the circuit is fed by a 20 amp breaker, you new length of cable must be #12 or heavier. #14 is Ok if it is a 15 amp breaker. Depending what else is on the circuit, you may or may not be able to use a very heavy load on the new outlet.

If tkrussell differs with me on a detail, take his word. There are some other good people here, but many here are best ignored.

I have a voltmeter. I am only going to be plugging in a shop light.

I'm trying to do the same thing...I don't understand about connecting to other whites when there are only the black and the other marked black. Can I just make the black go through the outlet before the switch? But it is at the end ot the run. I am stymied.

As I explained in my first answer, there are 2 ways to wire a switch and a light. If you have 2 cables at the switch, you can tie in an outlet just like I explained. Depending which black you connect to, the outlet may or my not have power when the light is off. If the switch only has one pair of wires plus a ground, you can't power anything from it. You will have to go to the light as explained in the first answer.

I tied into my switch by unscrewing connector with white wires and attaching new white going to new outlet and unscrewing black on switch and adding new black going to new outlet. You can do either top or bottom screw which determines whether the outlet is controlled by the switch or hot all the time. Be sure to turn off the breaker. I have mine controlled by the switch since I have a light plugged into the outlet and want to be able to turn it on without having to plug in or unplug it when I want it off. Don't forget the ground wire-you can tie into existing ground on switch.

Patty, you didn't put two wires under the screw did you? That's a no no. Use a pigtail instead. Fasten one end of the pigtail to the screw, and wirenut the other end with the blacks going to your light and receptacle. If I misunderstood you, or the switch is designed to accept two wires on one terminal, I apologize.

Sorry about that-I did pigtail it.