Need help Hacking an iGo Power Adapter

[tiger102]

Hi. I hope I am at the right place with the following query. I am new to this site and this is my first post. (As will probably be apparent from what follows. my knowledge of electronics is very rudimentary, being limited to basic circuitry that I studied many years ago to acquire a Ham Radio licence.). 
I am trying to make a home-made styrofoam "hot wire" cutter, based on a Youtube tutorial that I came across some time back. For the power source I decided to use an old iGo power adapter that I had, as this appears to deliver the level of current recommended.  However, when I cut the iGo wire to remove the connector tip, I find that - instead of being presented with two individual wires to give a positive and negative (or "feed" and "return") - I have a confusing mix! Specifically, there is (a) an outside silver multi strand wire, and (b)a silver paper-type wrapper, both of which surround 4 individual colored wires, as follows: (1) a white covered multistrand wire - quite thicker in diameter than the other three; and (2) three other, slimmer wires - one green, one brown and one yellow. Can somebody please let me know which wires I need to use to complete the circuit, which uses a used guitar wire (high E) as the burning element.  Many thanks in advance, and apologies if I have posted this in the wrong section.   

[PA0PBZ]

This one?

http://www.instructables.com/id/Hacking-your-iGo-Universal-Power-Adapter/

[tiger102]

Many thanks for replying to my enquiry. I have read the piece you directed me to but I'm afraid I was not able to understand from it which wire/s to use for (+) supply and which for (-). I'm afraid it was pitched at a level beyond my comprehension. But sincere thanks for taking the time to assist.

[fleuroman]

that's because Apple hate their consumers  ... the iGo has current and voltage limiting, because all Apple products talk to the charger. You cant just use v+ and v-... the iGo needs to know what voltage is required by the device, and how much current it's drawing.