It's easy to do. But!
Dont touch the contacts in the connector as the ballasts have a large capacitor that can still have charge when off but they are quite recessed so you have to try to hurt yourself.
Dont touch the glass on the bulb as oils in your skin can cause a hot spot and cause the glass to crack just like halogens.
Before you shell out £60+ on a bulb make sure the ballast or fuse is not the failure part. Best way is to swap the bulbs. (Halfords do a D1S quite cheap £60, but euro car parts do Philips for £90 ish but is a much better bulb)
If both stopped working at the same time you may need to look further up the chain.
I recently had an OE ballast fail on mine. It started flickering randomly, then it would only come on for a few seconds, than would not come on at all. Took bumper off, headlamp out, ballast off headlight, opened ballast (4 screws) quite abit of moisture was inside and the terminals wee shorting/ corroding. the PCB is stuck to the base with silicon and can be carefully levered off.
cleaned it all up and checked all the tracks and contacts (luckaly it had not got too bad) put it back together (used non corrosive silicone (rs) to reseal and stick pcb.) and it all works.
The whole job took about 2 hours. It was probably luck on my part that is was not to far gone but given the cost of a new ballast it is worth a try before you buy.
Last edited by sketchy19; 17-01-16 at 10:35.