I've posted this elsewhere, but oh well.
You'll likely run into the infamous ''soft start'' circuit. (Assuming the HID's will be installed into the headlights) The headlight circuit is not a conventional on/off circuit, it's a transistor driven one to make it easier on the light bulbs. (By eliminating the high inrush current on a cold filament)
So... the HID's start up okay, they just won't shut down. They'll flicker and not restart when you turn the lights on and off. (Or when the computer decides to turn them on/off) That's because the circuit hasn't shut down all the way, and the HID's can't reset and/or restart. The key off for a while or unplugging the HID ballasts lets them restart. Or... you turn off the lights, and the HID's flicker for the next minute or so.
The flickering problem is BAD for the HID's because they're trying to restart themselves with not enough voltage. The ballast can't take that for very long, so the problem MUST be dealt with before installing them into the low beams.
I'll have to try this idea in the next few days when I get time. I think a load resistor will cure the crap. There's plenty around this radio shop to use for experiments. A source for them can be found here: http://www.superbrightleds.com/tail-brake-turn.html
Look at the bottom of the page at their load resistors. A lot of vehicles depend on the current of a light bulb, and the resistor can ''fake out'' burned out bulb detection and the like.
I'll post my findings in the next few days on this and the other HID threads. As for now, my new Surco roof rack is waiting for me at home.
The HID problem can wait.