Are both inner (trunk lid) and outer (fender) brake lights not functioning? If so, most likely you don't have a light issue but a wiring problem. If only one is out, then it may be a bad light but also may be a bad connection at the light or upstream.
I'd start by pulling trunk panels (there may be a small one behind the outer taillight) and checking with a voltmeter before suspecting the lights. Pin 5 is hot and pin 2 is ground for the brake light on all four taillight light connectors.
One wire (from under the dash) feeds all five brake lights. It is split at a connector behind the rear seat and one below the left brake light. A wire then runs across the back of the trunk to the individual right side lights.
If both right lights are out, I'd check for voltage on pin 20 of connector FF01 (obviously while depressing the brake pedal).
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You can find the service manuals along with schematics with a Google search.
Toughest part of this is getting the panels off. If I remember right, you'll end up pulling the deck lid panel to get the side panels out. No fun.