Electrical/ Tail Light Problem

So, for a while all the tail lights worked on my 2001 Chevy Cavalier.

Then one day 3 brake lights didn't work. Two were the trunk that when replaced worked. Third was the brake light on the drivers side. When I replaced the bulb it still did not work. Keep in mind all the other lights did.

Just today I noticed that both the rear brake lights did not work. After I had tested my emergency lights, the passenger side brake light worked again.

Is this a wiring problem? Or a fuse problem? How would I tell if it was one of those? How do you tell if a fuse is bad?

I'm not sure I fully understand which lights are working/not working but this sounds like a wiring/connection/bulb issue. Most of those lights would be on the same fuse, so none of them would work if the fuse blew.

To test a fuse you can simply pull it out and look through it (assuming the casing is clear). There should be a little U-shaped band of metal running continuously from one side to the other with no breaks or scorching. You can also get a little ginchy battery powered device for testing them while still in the fuse block, by simply pushing the device's prongs against the fuse. Lastly, you can test both fuses and bulbs with an ohm- (or multi-) meter. Fuses should have a resistance rating of 0, and bulbs should have continuity...basically any reading but OL (open line).

Make sure you have the correct bulbs in place, and firmly seated. If they still don't work test the bulb with an ohmmeter. If they check out okay, test for voltage at the plug. You should be able to work your way back to the problem like this.

P.S. remember that most of these bulbs will have two filaments, make sure they're both ok

You can do the same thing that "fuse tester" does with a test light, and they're much cheaper. Just connect the clamp to ground and probe both sides of the fuses, if it lights on both sides, the fuse is good. If it lights on one side, the fuse is blown. But like goser said, doesn't sound like a fuse issue.

I don't really understand which lights are on/off either. Maybe a quick sketch would make it more clear.

Ok well sorry for taking a while to post, this is not my exact car but it shows you which lights work and doesn't. The R brake light used to work, then it started to short out, then it stopped working all together. Took it to a mechanic for a diagnostic, after about an hour they told me it needs get a new combination switch in order for the brake lights to work. And that it will cost 310$ to be exact for everything.
http://img51.imageshack.us/img51/339/cavac.jpg

The combination switch is a definite possibility, I've seen several that caused similar problems.

So I decided to get it repaired after talking the guy down to a more reasonable price, and now the brake lights work, lol. now all is left is to find a car seat clip for the passenger side