You have to remove the yellow plastic button to access a securing screw holding the switch and the cable asembly. This is not easy!
Make sure that the power lead is disconnected.
Each side of the yellow button is triangular with a blip on the bottom back corner which acts as the pivot point and retaines the button in place. Slide two thin but strong flat blades i.e. old dining knives down the side aimed at an angle towards the bottom corner pivots, lever the handles apart to squeeze togeather the sides of the buttons whilst with your third hand prise the front of the button up. If your lucky the button will pop out, possibly followed by a short spring, without anything breaking. A T5 (I think) screw can then be accessed to release the switch and cable assembly. This may need to be levered out since is is a slide fit into the top of the wand. Note it would appear that the cable/shroud/grip/switch is an integral unit and a Dyson replacement is required unless you have the means to add a suitable cable fixing and termination.
Not knowing the design of the unit I initially accessed the button area by removing the tool holder moulding but this will cause some damage to the plastic at the top of the handle on the moulding. I removed the top of the moulding which accommodates the tools by releasing one T5(?) screw which holds the lower part of the moulding to the wand, the other end i.e. top of the handle is locked by a groove on the switch assembly (Hence somethings got to give) however by gently levering the top up and outwards it is possible to remove the top with only breakages to the sides of the moulding on the handle. It is then possible to insert a long screwdriver up underneath the button to assist in separating it from the pivot points. Watch out for the spring also flying out when the button pops off.
Best of luck!!!
George Towns
February 2007