ghost in the courtesy light...drivin me nuts!!Please help!!

Ok.....this goes beyond weird and annoying ...I was driving in to work when stopping at traffic lights, my courtesy light came on....didn't think a whole lot of it, however when I pressed on the brake and began to drive away the light turned itself off. Same thing happened again at the next lights....and can you guess what happened at the next?lol
When I parked my car there was a few things I tried to fiddle with in the parking lot, one I noticed that the light was actually staying off, so for the heck of it I played around with the key and the light came back on (while the car was running), continuing to play with the key did not turn the light off however.
Now I had new keys cut for the car a couple weeks back, but havn't had the problem before, so I'm looking for advice on wether or not anybody thinks this is most likely caused by a bad key....or a short somewhere, and if it is a short does anybody have any ideas of narrowing down the search, or any tests to confirm the short location. Thanks in advance!!!