I am planning to upgrade my halogen headlamps with an aftermarket Xenon conversion kit. I read that it needs to be earthed otherwise there might be a problem with it.

Could anyone explain to me why is this earthing requirement needed?

I thought they were 'Plug n Play'??

Plug and play for me.

Mine was p & p too. Are you possibly mixing it up with canbus/resistors/error cancellers?

No seperate earth required. All connections made via wiring harness.

Look here

You are correct in thinking it can cause loads of trouble. It has been covered several times, but here is the first thread I found (by using the search facility on here)

Windscreen wipers fault

More info here

Don't use the 'CANbus' canceller type (which hang a very large capacitor across each supply to the light unit). Use the non-CANbus type and code controller 9 for Bi-Xenon. I doubt earthing the ballast will make much difference.

Does anyone know if this is a problem as well if one wants to add a full-beam Xenon-kit to an Octavia II with original Xenons?

AFTER MARKET HID ARE ILLEGAL SAVE YOUR MONEY AS IF YOU GET STOPPED BY THE LAW THEY WILL TELL YOU TO TAKE THEM OUT PLUS YOU HAVE TO CONVERT THEM BACK SO YOUR CAR CAN PASS ITS MOT

AFTER MARKET HID ARE ILLEGAL SAVE YOUR MONEY AS IF YOU GET STOPPED BY THE LAW THEY WILL TELL YOU TO TAKE THEM OUT PLUS YOU HAVE TO CONVERT THEM BACK SO YOUR CAR CAN PASS ITS MOT

Stop Shouting mate!

I just knew it wouldn't be long before somebody jumped on and kicked off the legal warning................

Although I disagree with any post full of shouting, I still feel it doesn't hurt to mention the legallity.

There are honestly people who don't know what they are doing can cause an MOT failure from 2012.

People see others doing a conversion and jump in without knowing exactly what could happen.

I guess once 2012 gets here and we see the first few MOT failures people will be better informed.