The brake lights of the 2003 Chevrolet TrailBlazer can malfunction for three main reasons: loose electrical connectors, faulty bulbs, or a faulty fuse. Thankfully, the solutions to these issues are fairly simple. The TrailBlazer uses a 3157-type bulb for its brake light and a 15A fuse for its brake light fuse. As the brake lights are very important for your TrailBlazer's safety, it is important to keep them in working order.
Turn the TrailBlazer's engine off, and open the lift gate of the vehicle.
Remove the two assembly screws from the lamp assembly, and pull it away from the TrailBlazer.
Pull on the wiring harness connected to the tail lamp assembly to make sure it is securely plugged in. If it is not, plug it in, and test the brake light. If it is still malfunctioning, it may be a bulb issue.
Unclip the TrailBlazer's wiring harness, and remove the three socket retainer screws with a Phillips screwdriver.
Remove the bottom socket by releasing the retaining tabs. Pull the bulb out of the socket, and use a paper towel to install the new bulb in its place. Place the socket back into the assembly, and reattach the wiring harness.
Place the assembly back into the vehicle, and reattach the two assembly screws and close the liftgate. Test the brake light. If it is still not functioning properly, the brake light fuse may need to be replaced.
Turn the TrailBlazer's engine off, and open the hood.
Remove the cover from the fuse box behind the battery, and locate the fuse labeled "Stop Lamp" in slot No. 12.
Remove the "Stop Lamp" fuse. Examine the fuse. If the metal wire is broken, then the fuse needs to be replaced. Replace it with a new 15A fuse.
Place the fuse box cover back into its initial position, and close the hood.
