What Trevor said is right......if you go with the 35W ballast you'll get plenty of light and not put additional load on your low beam lighting circuit. I just installed the 35w VVME HID's on my 2008 and went directly to the low beam lamp plug for the power. No relay, and they are working just fine. I'd avoid the 55w version, its overkill, and more load on the wiring. If i went with the 55w for any reason, i'd consider adding the relay to carry the extra load.