This question concerns a 2007 Trailblazer LS. My brake lights fail to illuminate when the brake is pressed. The center mounted brake light illuminates, the turn signals work as does the back up lights. The fuses and bulbs are good. I replaced the tail light circuit boards, but still am not able to get lights to work.

The instrument panel cluster (IPC) illuminates the CHECK GAS CAP indicator in the message center when the gas cap is not tightened properly or not on the filler neck.

Do you know how to test using a DVOM - digital volt ohm meter ? Is there B+ voltage going into the brake light switch ? An coming out when the brake pedal is pressed ? What fuse's ? There is only one fuse for the brake lights !
The BRAKE SW fuse in the RH I/P fuse block supplies battery positive voltage to the normally-open stop lamp switch. When you press the brake pedal the switch contacts close and battery positive voltage is supplied to the left and right stop lamp assemblies and to the center high mounted stop lamp (CHMSL). The left and right stop lamp along with the CHMSL are grounded at G302.
Do you know about the right insturment panel fuse box ?
Stop Lamps Inoperative
Step
Action
Yes
No
Schematic Reference: Exterior Lights Schematics
1
Did you perform the Lighting System Diagnostic System Check?
YES - Go to Step 2
NO - Go to Diagnostic System Check - Lighting Systems
2
Press the brake pedal.
Do all of the stop lamps illuminate?
YES - Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems
NO - Go to Step 3
3
Are all the stop lamps inoperative?
YES - Go to Step 4
NO - Go to Step 7
4
Inspect the BRK SW fuse.
Is the fuse open?
YES - Go to Step 14
NO - Go to Step 5
5
Disconnect the stop lamp switch.
Using a test lamp connected to ground, probe the battery supply voltage circuit of the stop lamp switch connector.
Does the test lamp illuminate?
YES - Go to Step 6
NO - Go to Step 13
6
Install a fused jumper between the battery supply voltage circuit and the stop lamp switch signal circuit of the stop lamp switch connector.
Do the stop lamps illuminate?
YES - Go to Step 12
NO - Go to Step 17
7
Determine if the center high mounted stop lamp is inoperative or the stop/turn lamps are inoperative.
Are the stop/turn lamps inoperative?
YES - Go to Step 8
NO - Go to Step 9
8
Do the turn lamps operate normally?
YES - Go to Step 17
NO - Go to Turn Signal Lamps and/or Indicators Inoperative
9
Disconnect the center high mounted stop lamp.
Using a test lamp connected to ground, probe the stop lamp switch signal circuit of the center high mounted stop lamp at the harness connector.
Press the brake pedal.
Does the test lamp illuminate?
YES - Go to Step 10
NO - Go to Step 15
10
Using a test lamp, probe between the stop lamp switch signal circuit and the ground circuit of the center high mounted stop lamp with a test lamp.
Press the brake pedal.
Does the test lamp illuminate?
Go to Step 11
Go to Step 16
11
Inspect for poor connections at the harness connector of the center high mounted stop lamp. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Step 20
Go to Step 19
12
Inspect for poor connections at the harness connector of the stop lamp switch. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Step 20
Go to Step 18
13
Repair a open or high resistance in the battery supply voltage circuit of the stop lamp switch. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you complete the repair?
Go to Step 20
--
14
Repair a short to ground in one of the following circuits:
• The battery supply voltage circuit of the stop lamp switch
• The stop lamp switch signal circuit of the stop lamp switch
Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you complete the repair?
Go to Step 20
--
15
Repair a open or high resistance in the stop lamp switch signal circuit of the center high mounted stop lamp. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you complete the repair?
Go to Step 20
--
16
Repair an open or high resistance in the ground circuit of the center high mounted stop lamp. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you complete the repair?
Go to Step 20
--
17
Repair an open or high resistance in the stop lamp switch signal circuit of the stop lamp switch. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you complete the repair?
Go to Step 20
--
18
Verify the stop lamp switch adjustment. Refer to Stop Lamp Switch Adjustment . If OK, replace the stop lamp switch. Refer to Stop Lamp Switch Replacement .
Did you complete the repair?
Go to Step 20
--
19
Replace the center high mounted stop lamps. Refer to High Mount Stop Lamp Replacement .
Did you complete the repair?
Go to Step 20
--
20
Operate the system in order to verify the repair.
Did you correct the condition?
System OK
Go to Step 2

First you need to have EBCM - electronic brake control module check for DTC'S - diagnostic trouble code's . If the light is on there is a code stored . I think most part stores can do this and for free . After you find out what code is stored , looking up that code in service repair information for diagnostic trouble shooting chart would be next step . There are a few codes too.
DTC C0035 or C0040
DTC C0045 or C0050
DTC C0110
DTC C0131
DTC C0161
DTC C0186
DTC C0196
DTC C0201
DTC C0240
DTC C0241 or P0856
DTC C0244 or P1689
DTC C0245
DTC C0283
DTC C0287
DTC C0290 or C0292
DTC C0455
DTC C0550
DTC C0558

Find the code do the diagnostic's , fix the problem , wiring issue's , a sensor , bad module ,what ever it is . The light will go out then . Here is a sample of code discription .
• DTC C0035 Left Front Wheel Speed Sensor Circuit
• DTC C0040 Right Front Wheel Speed Sensor Circuit

There is ALWAYS a reason.
Reasons that the ABS light will illuminate:

1. Brake pads, brake shoes, rotors, or drums worn beyond allowable specification;
2. Brake fluid level low, or brake fluid leaking;
3. Failed ABS control unit;
4. Failed ABS sensors at wheels

****, you can check some more but from what I am reading your problem could be related to a faulty ignition switch. I am sending you a copy of some fixes.. you can compare to your condition..
Best of Luck to you..

2006 Chevrolet Trailblazer LS 4.2L, Vin S, Eng Cfg L6
Customer Concern: No blower motor function. AntiLock Brake System (ABS), Red Brake Warning Light (RBWL), Traction lights all on. Radio does not work. Tests/Procedures: 1. Check for battery voltage at fuses #31 and 39 in Rear Fuse Box under the rear seat.

2. If the voltage value is less than battery voltage, check the Orange wire at the 48 cavity connector located at the base of the steering column at pin D1.

3. If the voltage is low at C201 check the voltage at pin "G" of the ignition switch.


Potential Causes: Ignition Switch


2006 Chevrolet Trailblazer LS 4.2L, Vin S, Eng Cfg L6
Customer Concern: ABS, Low track light comes on intermittently. The heater blower motor quits running, 4WD not working. No communication with the ABS. If you disconnect the ABS computer and plug it back in, it may work. Tests/Procedures: 1. Test voltage at HVAC 30A, 4WD 15A, HVAC 1 10A, BRAKE 10A, TBC RUN 3A labeled fuses in the rear fuse block during the problem.

2. Inspect connector 101 38 cavity connector mounted along the underhood bussed electrical center. This harness may be routed tightly around the underhood fuse block, causing chafing or connector terminal contact that could induce any of the concerns listed.

3. Clean and secure ground G110 located on the lower left side of the engine block. Potential Causes: Damaged Circuit 300
Damaged Connector C101
Improperly Installed Engine Compartment Harness
Malfunctioning Ignition Switch

The switch is fine if the third brake light is functioning. Even though the tail lights work, the filament for the brake light can be burned out. Sometimes they look intact but are still burned out. Replece the bulbs.

Remove the tail lamp housing and test for power at the wiring connector. Does the center high mount stop lamp operate correctly? The lamp circuit boards have seen many problems.

sounds like a problem in the abs brake system, you will need to take it to a dealer to be diagnosed.. it probably won't cause any driveability issues but is definitely a safety concern..

LH/RH lights cable could be disconnected anywhere, will take a long time to trace.
Center Brake Light and LH & RH should be connected at one point.
Jump a cable from Center Brake Light to one of Rear Break Light.
Hope this will works.

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?