As Foxy's web site is no longer available here is the original guide taken from the web archive: It is back online again, see link further down the thread 
Existing wires:
Blue-white Blue-red Brown
Insert wires into only pins 1, 3, 4 & 5.
New wires connect to existing as follows:
New wire to pin 1
Blue-white to pin 3
Brown to pin 4
Blue-red to pin 5
Pull the plug from the back of the instrument light Dimmer/Headlight adjuster unit.
The purple wire, next to the brown is the illumination wire that I used - not dimmed.
Use a skotch-lok or cut, solder and heat-shrink like this.
Another forum member has kindly noted that the light is a very tight fit, as the insulation behind the headlining partly interferes with the new plug when you push the light up into the aperture.
To quote his guide:
"When reinstalling the panel, I found it was very tight - infact too tight. I found the extended plastic for the wiring plug on the panel is fouling with some insulation in the headlining. There isnt enough room for it to basically push back and the the metal clips push in. So I had to cut off a piece of the polystyrene foam insulation, just hacked it with a stanely knife. I made a little section, so the wiring plug can sit in there perfectly."
Thanks to Aamer!
Total cost: Approx £25 GBP
Time taken - 30 minutes
Part numbers:
Light: 3B7947105F2EN
Plug: 3B0972706
Wires: 000979131A - two off required.