Oh, make sure your light switch works too. You can test this by popping the cover off the light (like you do when you're changing bulbs). The switch will have 3 positions - On, Door, Off.
In On position it grounds on the roof of the car, the light should be on.
In Door position it tries to ground to the door switches. You can try to ground this terminal, and the light should come on.
In Off position it doesn't go anywhere.