call the dealer and ask to speak to parts depot.
Tell them you have this strange piece of plastic with a part number on it, and "would you be a sweet guy and look up what this thing is?" They have computers back there to do this.
Use a sweet convincing voice if the dude's busy. 99% of guys will bend over backwards in the telphone to help a female voice on the other line.
oh yah: I have no clue what that is... and I've ripped apart my trunk multiple times trying to fix my freaking tail light problems.