You can check the relay, or you can pull upper trunk panel and check to see if you see a break in a wire. The wire harness may be cut by wear and tear.
〉 Answered on Jul 16th, 2008 by Amanda J. Pierce, MBA "AJ", Certified Mechanic, Project Coordinator; Primavera Scheduler at VIGOR Alaska Industrial Shipyard & BizzM3ch Solutions
It's possible that there is a problem with your multifunction turn signal switch (MFS). Only the rear brake lights go through that switch, not the center one.
I've read where the hazard part of the turn signal switch going bad causes this problem.
You might want to check that. If not, check your wiring. It could be something as simple as a bad ground. Good Luck.
〉 Answered on Jul 16th, 2008 by Lori Johnson, Owner and Instructor at Ladies Start Your Engines