I understand that most the replies here are at best 3 yrs old. However, in my lengthy search I came upon this website when I couldn't understand why the brake lights in my '02 Trailblazer LS didn't work but my 3rd brake light did?!? I solve my issue after several days of searching for the answer when it turned out be so simple!
The '02 Trailblazer has a SECOND fuse block under the drivers side back seat. If you still have your manual, it will show you a diagram of it (mine is on page 6-61). There, unlike the fuse block under the hood, this one I.D.'s each fuse. Take a look at #34 15AMP "VEH STOP". Also know that this control's your Cruise Control. I'll bet it's blown?
Ii replaced this fuse and VOILA, ALL brake lights AND cruise control work again, good luck!!