I dunno exactly what sorta plug you have, but I gave this a look through and it seems reasonably sound:
http://www.instructables.com/id/Make-Cu ... /?ALLSTEPSHe was overzealous with the heat shrink. That first bit that goes over the whole thing is really all you need. If you have the kinda plug that clamps the wire down, you don't need any heatshrink at all (Many would disagree, but they're wrong). His soldering was a bit sloppy as well. He should have used a larger tip so he could tin the wires faster, but sometimes you gotta make do with what you got, and the way he did it really won't cause any problems.