Accessory lights - how to?

I want to add a lighted wreath on the front of my wife’s Trailblazer. The cord of lights that comes with the wreath is 12v and has a lighter plug on the end. The accessory and lighter sockets in the car seem to operate even when the car is off. I want to tie the wreath lights into somewhere in the engine compartment rather than bring the cord through the firewall and then risk forgetting to unplug it sometime and draining the battery. Where can I tie the wreath lights into that will operate only when the vehicle is on? Any help would be greatly appreciated.

by the way it's a 2004 Trailblazer

Take about 25-30 bucks and get yourself a 4-channel wireless keyfob for it. You can get them on cardomain.com (the link is below), then you can go wild with your creativity. That's the switch I use for my underbody lighting kit. Don't let the reviews sway you away either. I debated for months before I got it because of the reviews, but after talking with some people on the StreetGlow forums, they all had good luck with them. I've had it for about six months and no problems what so ever. Good luck.

http://www.cardomain.com/item/PILPLSW29