I have a 2003 Oldsmobile Aurora. On the rear panel right behind the wheel there is a red reflector thing that looks like a light, it is oblong and just snaps into the panel, What is this thing called?
Reflector.
Tester
Or “Side Marker” reflector.
Since you said “right behind the wheel”, I am assuming that the panel that you are referring to is the rear fender. If that is the case, then the piece to which you refer is called a Side Marker Light. Or at least, that is what I have always called it.
The part is mounted in the rear bumper cover. If there is wiring running to it it is a rear side marker lamp. If there is no wiring runing to it it is a rear side reflector.