Marker light, usually. I've seen stuff like that before, I'm tempted to dig through some wiring diagrams and just figure it out myself.

http://www.grandprixforums.net/threa...14#post1440814

There's the info, if you want to look for it yourself. I'm gonna have a look and see if I can find what wires go where... I'll post it up if I don't find a thread.