1. Identify the Problem:
* Which lights aren't working? Are both brake lights out? Just one? Are the turn signals affected? Knowing the specifics helps narrow down the possibilities.
* When do they fail? Do they work sometimes and not others? This suggests a possible intermittent connection problem. Do they only fail when the brakes are applied? This points towards a brake light switch issue.
2. Simple Checks (Before diving into complex wiring):
* Bulbs: This is the most common cause. Check all brake light bulbs and turn signal bulbs. They can burn out without warning. Replace any faulty bulbs with the correct wattage.
* Fuses: Check the fuse box (usually under the hood and/or inside the vehicle) for blown fuses related to the brake lights and turn signals. Your owner's manual will show you a fuse diagram.
* Brake Light Switch: Located near the brake pedal, this switch activates the brake lights. You can test this with a multimeter or a test light. With the brake pedal released, there should be no continuity (circuit closed). When you press the brake pedal, there should be continuity. If not, the switch needs replacement.
3. More Advanced Troubleshooting:
If the bulbs and fuses are okay, and the brake light switch is working, you'll need to delve into the wiring:
* Wiring Harness: Inspect the wiring harness connecting the lights to the vehicle's electrical system. Look for any damaged, corroded, or disconnected wires, especially near the tail lights. Pay close attention to areas prone to chafing or wear.
* Tail Light Assemblies: Sometimes the connections within the tail light assemblies themselves can corrode or become loose. Carefully inspect the sockets and connections inside the taillights. Cleaning them with contact cleaner might solve the problem.
* Grounding: Poor grounding can cause all sorts of electrical issues. Check the ground connections for the taillights. These are usually metal tabs or screws that connect the light assembly to the vehicle's body. Clean them and ensure a secure connection.
* Turn Signal Switch: If your turn signals aren't working, a faulty turn signal switch (located on the steering column) could be the culprit. This requires more advanced electrical testing or replacement.
* Hazard Lights: Test your hazard lights. If they work, it suggests the bulbs, fuses, and some wiring are okay. If they don't work, the problem is likely more widespread.
* Multi-meter: A multimeter is invaluable for testing voltage and continuity in the wiring. This will allow you to pinpoint exactly where the circuit is broken.
4. Getting Help:
* Repair Manual: A repair manual specific to your 1996 GMC Jimmy will provide detailed wiring diagrams and troubleshooting steps.
* Mechanic: If you're not comfortable working with car electrical systems, a qualified mechanic can diagnose and repair the problem efficiently.
Remember safety first! Disconnect the negative battery terminal before working on any electrical components. Always refer to your owner's manual for specific information about your vehicle's electrical system.
