I have used magnetic tow lights on both of my toads. First was a 1998 Chevy Tracker. I made two metal plates that I glued to the back bumper for the magnetic lights. My current toad, a 2006 HHR did not have a place for the metal plates so I used them on the roof and on several occasions one or the other would get blown off. Recently found a wiring system by Hopkins on the website below. This is a "plug and play" system that installs by unplugging each of your tail lights and plugging this system in between the car wiring and the taillights. The diodes are in a small box that you attach with sticky tape. It comes completely wired with a four prong plug and plenty of wire to run under the vehicle. The only thing you have to connect is a ground wire. I recently installed the system and it was very easy. (Note: the ground is very important!) If you do a search on this website to find the correct item for your vehicle and then do a google search you will find it much cheaper on Amazon or EBay. Can be easily removed if needed for warranty of the vehicle.
Good Luck!
http://www.etrailer.com/Tow-Bar-Wiring/Hopkins/HM56100.html