In stock configuration, the halogen bulbs only light up when you pull the turn signal stalk to flash your headlights (flash-to-pass) when the headlights are off. It's designed this way because halogen bulbs can light up faster and it's not good for the xenon bulb to be flickering on/off. When the normal HID headlights are on, the flash to pass just raises the low beam shield so that it becomes the high beam. When you switch to high beams, the shield stays up. When the normal headlights are on, the halogen is never used.
This mod lets you have both high beam xenon (shutter raised) and the high beam (flash to pass) lights on when you switch the headlights to high beam. Before anyone says this is dangerous, this is how many models of cars are from the factory with DOT approval and you shouldn't be blinding other cars with high beams anyways. It doesn't take a genius to know that having more headlights on will result in more light.
While you could also have the foglights on with high beams, it's illegal to have more than 4 lights lit on the front of the car in the US. Disclaimer: do not do this modification if it's illegal where you live and drive. See the TOS Agreement for the full legal disclaimer.
Note - if your HID headlights were retrofitted, you must do the optional trigger shutter wire from the headlights to the CECM for the headlight mod to work.
This mod first requires your instrument cluster code to be changed from "American to "Great Britain", see below for details. It isn't possible to do the headlight mod with a North American coded cluster. This also removes the door open chime and changes temperature to C, calculated mpg to UK gallons, and 12 hour clock to 24 hour clock. These can all be adjusted back to US settings. See 1000q: MFD settings for more features. If your car doesn't have a highline cluster I'm not sure if you have the MFD settings screens. It also removes the "accept" acknowledgement when you turn on the OEM VW MFD2 navigation system. See 1000q: MFD2 FAQ for more info on the GPS system. As of 2010, the latest firmware update for the MFD2 GPS system is version 50.
Change the instrument cluster code to UK or GB (Great Britain). For more details, see 1000q: disable door chime.
Go back to the main screen and click on "Cent. Elect." to enter the central electric control
Click on "Coding" (Ignore the Adaptation box, the screenshot is
from another writeup). Then click on "Long Coding
Use the right arrow button to go to "Byte 17" and uncheck
"Deactivation of Additional High Beam with Bi-Xenon". Again,
your cluster must be coded to UK for it to work or else it won't do anything.
You could uncheck the box marked "Front Fog Lights deactivated with High Beam" but having lights down low when you want to focus on longer distances is counter productive and degrades night vision. It's also illegal to have more than four lights on at the front of the car.
Close the long coding and it'll automatically copy/paste your new code (the yellow code at the top) to the right place. Click "Do it!" to save and exit the module.
If you have any questions about this procedure, feel free to ask at the myturbodiesel.com forums or search the site below: