I've had some experience with the Arduino via a EE degree in college. You're probrably better off at an Arduino forum. They will help with any and all coding questions you have. As far as the harware goes, I doubt the arduino itself has enough capacity to drive the current that the tail lights require. That being said, It isn't impossible, just a lot more difficult than you think. You will most likely have to run the LEDs through some sort of relay system using the arduino's low level signals as inputs on the relay. There are also several add-on kits produced for the arduino, so there may be a kit that could help you do this.
06' SW tC