I have a 2003 Mazda 6. A few lights aren't working: my third break light, the license plate lights, and the front outer marker lights. I changed the bulb in the third break light, didn't work.

SOURCE: brake lights/rear turn signals

I had the same problem with my 1999 Yukon. The electric board needed to be replaced. Rust starts to build up and shorts out or blows the bulb. The dealership charged $73.60 for the part and I installed it myself (Saved $30).

SOURCE: license's plate light stopped working even with new bulb.

It wouldn't be a fuse if that's the only light that's not working, I believe all of the parking lights are on the same fuse. It's most likely a bad ground or corrosion inside the socket where the bulb makes the electrical connection. So check the socket to make sure it has no corrosion, if it does, clean it up and apply some dielectric grease (available at any parts store) to prevent future corrosion, and check for a loose or broken ground wire.

SOURCE: license plate bulb needs replacing

Remove license plate. Unscrew the screws on the underside of the bumper. Slide the lights back toward the trunk and then down through the opening. Unscrew bulb and replace with a new one.

Reverse steps to reinstall the lights.

SOURCE: 2001 GMC Jimmy break lights not working but all

Check the brake light switch should be a orange wire with 12v then a white wire with 12v when the pedal is pressed.If htat cks good then ck the hazard switch by moving it up and down and wiggeling the knob with the brake pedal pressed if they start working then your multifunction switch is bad and needs to be replaced.

Testimonial: "We check and you were right on the money. It's the hazard switch carrier. Thanks for you help."

SOURCE: Remove 2003 MAzda 6 parking light bulb

http://forum.mazda6club.com/electrical/135367-changing-194s-headlights.html