1. Double-check the fuses: Even if they *look* fine, use a multimeter to test continuity. A fuse can have an internal break that's not visually apparent. Look for fuses specifically related to the tail lights or brake lights, not just a generic "lights" fuse. Consult your owner's manual for the correct fuse locations and ratings.
2. Check the bulbs: The brake light bulbs themselves could be burned out. Remove the bulbs and inspect the filaments. Replace them with new ones, even if they *seem* okay. It's a cheap and easy fix.
3. Inspect the wiring: This is the most likely culprit. Look for broken or corroded wires in the wiring harness leading to the taillights. Pay close attention to the areas where the wires enter and exit the vehicle body – these are common points of failure. Check for:
* Loose connections: Wiggle the connectors at the bulbs and the harness to see if you get intermittent light.
* Broken wires: Carefully inspect the wiring for any breaks or cuts in the insulation.
* Corrosion: Look for corrosion on the connectors and wire terminals. Clean them with a wire brush or contact cleaner.
4. Brake light switch: The switch, located near the brake pedal, activates the brake lights. If it's faulty, it won't send power to the lights. You can test it by measuring the voltage at the switch with a multimeter when the brake is pressed. A simple way to initially test this is to have someone press the brake while you inspect for power to the lights.
5. Grounding issues: Poor grounding can prevent the brake lights from working. Check the ground connections on the taillight assembly itself.
6. Brake light switch connector: Make sure the brake light switch connector is properly connected.
Using a Multimeter: A multimeter is invaluable for diagnosing electrical problems. You can use it to:
* Test fuses: Check for continuity across the fuse.
* Test voltage: Check for voltage at the brake light bulbs when the brake is pressed.
* Test for continuity in wires: Check for breaks in the wiring.
Important Safety Note: Disconnect the negative battery terminal before doing any electrical work to prevent accidental shorts or shocks.
If you're not comfortable working with car electrical systems, take your Blazer to a qualified mechanic for diagnosis and repair. It's safer and could save you time and money in the long run.
