Q: lights not working - 2003 Mazda Protege5

Hello. It sounds like there is some sort of short in the system. If you have had any work done on the vehicle, I would check for damaged wires in that area. If using a volt meter, check the available voltage at the taillight bulb’s socket. You should receive a full 12 volts. If there is not 12 volts, trace the wires backwards (or forwards from the fuse box if you prefer), looking for the spot that you lose voltage. Considering the dimmer switch isn’t working, you might want to check there (and any switches along the wires path), since switches are a common source of issues. If you would like to have this checked, a qualified professional from YourMechanic can come to your home or office to inspect the lights problem and have this addressed properly.