The description below is for the repair of the power cable on a Dyson DC03 but I think it also applies to a DC04 because I started out with an internet tip for a DC04 which was badly worded so hear is my slant on it.

All of the of the work below is done with the Dyson disconnected from the mains – of course.

Step one - Removing the Yellow Button

Normally the yellow button rotates on two pivots either side of the button (see Fig 1a)  The springiness of the plastic keeps these into two holes either side and retains the button into position.

Fig 1a: On/Off button

To release the button you have to release the two pivots from their holes by bending the plastic inwards. This is not easy! Slide two thin but strong flat blades i.e. old dining knives down the side aimed at an angle towards the bottom corner pivots. This is the tricky bit because you need to visualize where the pivots are located. If you press the button on and off a couple of times you can judge the centre of the rotating action. The holes at either side are also not just straight down in a flat piece of plastic (see Figs 2 and 3).

Fig 2: Left Hand Pivot Hole

Lever the handles of the knives outward to squeeze together the sides of the button.  If you can get an assistant at this point to provide the third hand you should be able to prise the front of the button up. If your lucky the button will pop out without breaking. There is also a short spring that may come loose but if you note where it is in Fig 1b it’s an easy thing to put it back. A T5 screw can then be accessed to release the switch and cable assembly which slides up vertically on guides. See fig 4

Fig 4: Anti-tamper Screw Holding in Switch Assembly

You may need to wedge a flat screwdriver in at the back where the pipe goes to help it start. 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. The cables are connected by crimp spade terminals. You can probably get these from a local Maplins, Tandy or RS Components. A car spares shop may also be able to help. Being a bodger of the old school with a soldering iron, I cut the mains cable back before the strain relief clip, re-threaded the cable and soldered the newly bared ends onto the ends of the crimp terminals. They are both covered with a shroud and the cable strain is taken by the long strain relief gland so I don’t think there will be any problem with this.