Its awkward. The cable goes into the machine under the on/off button. To get into this part you have to remove a screw and the cable, on/off button come away with the switch section. The problem is accessing the screw. Its under the button. You have to gently prise it out. If you look down the side of the button, the side against the body of the machine, you will see a little cut out in the plastic. If you can get some thin but stiff wire and push it down there you may be able to free the button. Theres a little hook shaped piece of plastic on the bottom of the button the locks into the body of the cleaner to prevent it springing out every time you switch on and off. Its that, that makes the job awkward. 9 times out of 10 you will break this little hook. I do these everyday, you can glue and melt it back together but it is fiddly, BE WARNED.
Once the button is out you'll see the screw, its a TORX screw, nothing is easy about a Dyson. Remove the screw and gently ease the cable upward will release that switch section of body.
Take note of how the cable gland is located and how the cable threads round the formers. When you replace the cable dont forget to thread it through the cable gland before you put it back together. Then its just a reversal of what you've just done. If you were lucky enough to get the button out without breaking it. It just pushes back in. I would suggest you give it rub round with sandpaper to smooth it off again as prising it out damages the sides slightly.
Have fun ?
steveD
April 2008