I just replaced my 2010 SL backup tail lamp. If it's just the wires you need to access. There are 2 panels at the back of your trunk door. Pop it out and you'll get to the wires. If you need access to the light itself. You have to take off 3 nuts. 2 on each side and 1 inside that panel that I just mentioned.
Then you have to pry the entire back up lens. Be careful not to break it. It is held on to the trunk door by a sticky rubber seal. Pry it out by working around the lens housing until it pops out. The entire back up housing will give you access to the wires, light bulb, etc.