2004 trailblazer left brake light

Tony, our TB's only have 3 bulbs, 1 brake, 1 running, 1 backup.
If you happened to be playing with NEW LED bulbs (from local retail location) for the brakes, guaranteed you blew the fuse under the rear seat. It takes a special CK socket for the brakes that no one carry's. If you're only dealing with normal incondecent bulbs, I'd still check the fuse under the rear passenger seat.

There was a recall on this, see your local Chevrolet dealer.... Recall Date: NOV 01, 2004 Model Affected: 2003 Chevrolet Trailblazer Summary: ON CERTAIN SPORT UTILITY VEHICLES, VIBRATION AND HEAT MAY CAUSE THE TAIL LAMP/STOP LAMP BULB TO LOOSEN IN ITS SOCKET. IF THIS OCCURS, THE BULB MAY FLICKER AND EVENTUALLY BECOME INOPERATIVE. Consequences: AN INOPERATIVE BRAKE LAMP WILL NOT CONVEY THE DRIVER'S INTENTION OF STOPPING TO DRIVERS IN FOLLOWING VEHICLES, AND AN INOPERATIVE REAR TURN SIGNAL LAMP WILL NOT CONVEY THE DRIVER'S INTENTION TO TURN TO DRIVERS IN FOLLOWING VEHICLES. BOTH OF THESE FAILURES CAN INCREASE THE RISK OF A CRASH. Remedy: DEALERS WILL INSPECT THE TAIL LAMP/STOP LAMP ASSEMBLIES, AND IF NECESSARY, REPLACE THEM. THE RECALL BEGAN ON NOVEMBER 22, 2004. OWNERS SHOULD CONTACT CHEVROLET AT 1-800-630-2438, OLDSMOBILE AT 1-800-630-6537, BUICK AT 1-866-608-8080, OR GMC AT 1-866-996-9463. Potential Units Affected: 871473 Notes: GENERAL MOTORS CORP. Read more: http://www.motortrend.com/cars/2003/chevrolet/trailblazer/recalls/#ixzz2jWJ1eDyR

Chances are that is the bulb. Its a dual filament bulb. The brake portion of it is burnt out. try swapping it with the left side and see if it works then. If it works, get a new bulb.

There were problems with the circuit board assemblies on the earlier years of the Envoy. Also check the socket for the brake light, make sure the contacts are OK.

If the top brake light is working, then the brake light switch on the brake pedal is ok and adjusted properly. GM had major problems with the circuit boards on these....check for power at the circuit boards with the brake pedal depressed.
Also,the brake/stop lamps are wired thru the Turn Signal switch which on this model is the multifunction switch...I have seen this fail many times, it's expensive and not a repair that can be made in a few minutes, takes several hours and a lot of paitence.
Did you check the fuses in the rear fuse box as well?...I suggest you call your dealer or GM direct and see if your vehicle falls under any of these recall notices---i bet it does. If the recall repairs have not been made, then they will do for you at no cost. You will need to have your VIN number ready when you call. Below is a brief description of a recall notice.

Recall Summary:ON CERTAIN SPORT UTILITY VEHICLES, VIBRATION AND HEAT MAY CAUSE THE TAIL LAMP/STOP LAMP BULB TO LOOSEN IN ITS SOCKET. IF THIS OCCURS, THE BULB MAY FLICKER AND EVENTUALLY BECOME INOPERATIVE.

Consequence:AN INOPERATIVE BRAKE LAMP WILL NOT CONVEY THE DRIVER'S INTENTION OF STOPPING TO DRIVERS IN FOLLOWING VEHICLES, AND AN INOPERATIVE REAR TURN SIGNAL LAMP WILL NOT CONVEY THE DRIVER¿S INTENTION TO TURN TO DRIVERS IN FOLLOWING VEHICLES. BOTH OF THESE FAILURES CAN INCREASE THE RISK OF A CRASH. RemedyDEALERS WILL INSPECT THE TAIL LAMP/STOP LAMP ASSEMBLIES, AND IF NECESSARY, REPLACE THEM. THE RECALL BEGAN ON NOVEMBER 22, 2004. OWNERS SHOULD CONTACT CHEVROLET AT 1-800-630-2438, OLDSMOBILE AT 1-800-630-6537, BUICK AT 1-866-608-8080, OR GMC AT 1-866-996-9463. NotesGENERAL MOTORS CORP. 04087

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The Trailblazers have a common problem with the printed circuit boards in the tail lamp housing.
Unplug the tail lamp housing at the wiring connector and test for power with a test light. ( With turn signals on) You may have an open circuit in the lamp housing circuit board. Good luck

check the ground wire, possibly in the back behind one of the access panels near the wiring harness

If the other side is working, then it will not be a fuse problem. more then likely it is a grounding problem or there is a short in the wire. Take a test light and check and see if you are getting a hot wire to the brake light. If it is hot then it is a grounding problem. Make sure that the bulb is in the right way and look for any corrosion where the bulb goes and clean it out.

The bulb actually has two seperate elements in it.
That is why the tail light works fine.

If you take the bulb out you will see the seperate elements.
Change the bulb and it should be fine.

I have the same problem with my 2004 Trailblazer LT. Driver side brake light does not illuminate. All other lights work fine. Replaced bulbs. Still does not illuminate. Cannot figure out which fuse goes to this light. Could it be a fuse?