Fixing a set of faulty tail lights will first entail identifying what's wrong with it. A good place to start would be checking the fuse box for a blown tail light fuse. This would ultimately be pretty easy to fix, as it requires only a replacement fuse. Once that's done, you can consider checking the tail light wiring. Specifically, take note of any loose connectors, frayed wires, or short-circuiting. If that doesn't fix it, then you might have to replace the tail light bulb. The initial steps might be rather tough since you'll need to disassemble the entire tail light assembly. But once you've done that, getting at the bulbs should be easy.