Darkwood

When you get to the second area of your playthrough, The Silent Woods, do some exploring until you find a place called "The Pig Shed". Once you find it, it will be marked on your map. Now what you need to do is get a cable. You can get one of these from Piotrek (whose house will have already been marked on your map through story progression). It will cost you 80 rep which is quite easy to obtain especially at this point in the game. Once you have your cable, head back to the pig shed and in the upper part of the complex you will see a severed power cable. Fix the cable with the one you bought, and follow the cables into the nearby open shed. Here you should find a lever and a generator. Make sure the generator is turned on and head back to the lever. Interact with the lever and choose the options in THIS order:

1. Remove lock
2. Set lever to the bottom
3. Push button

You should hear some electric sounds and some... other not electric sounds, and you'll get your achievement. At this point you can go into the other part of the complex to check out the other end of the cables if you wish as there are some great essence items in there.