tag light?

i know im the biggest greenhorn for cars, but i have a little dilemma. about a week ago i got pulled over because my tag light didnt work, so the police gave me this paper saying that i have to get it fixed and sent in by like thirty days. so i figure hey no sweat its only a tag light. i go to autozone and get the right light for my car and year. i swap out the old one for the new one and the tag light still doesnt come on:crying:

could it be a fuse, or wire or something?