The 2003 Kia Spectra had two fuse blocks, one inside the car, behind the driver-side kick panel, and one under the hood, to the driver side of the engine. The fuse for the brake lights, which Kia calls the stop light fuse, is in the fuse block inside the car. Checking the fuse is a quick and easy job that doesn't require removal of the fuse, given you have a continuity tester.
Remove the fuse cover -- the rectangular, plastic door -- from the driver-side kick panel, by pressing the unlocking tab, swinging the panel away from the kick panel and pulling the fuse cover from the kick panel. The stop light fuse is the bottom-most one in the center column. Press each probe of a continuity tester inside the small openings on the outer edges of the top of the fuse to check for continuity. If there is continuity, then the fuse is good, and no continuity means the filament in the fuse is blown and you need to replace it.
If you do not have a continuity tester, you can simply pull the fuse out, using a pair of needle-nose pliers or the fuse-removal tool in the under-hood fuse block, then visually inspect the filament for breaks. In some cases, a break in the filament is not detectable by the human eye, so using a continuity tester is always the most accurate checking process.
