To troubleshoot brake light issues, you'll need to check several potential grounding points:
* Tail Light Assemblies: The ground wire for each tail light assembly may be connected to the body of the vehicle near the light itself. Look for a bolt or screw that attaches the light housing to the body. This bolt often acts as the ground point. Check for corrosion or loose connections.
* Wiring Harness Connections: Check the grounds where the wiring harness connects to the body. These connections might be under the vehicle or in areas where the harness passes through the body. Look for corrosion or loose connections.
* Chassis Ground Points: There might be designated chassis ground points near the rear of the vehicle where multiple grounds are connected. These points are often large bolts or studs. Check for corrosion and ensure a good connection.
* Brake Light Switch: While this is less likely a grounding problem, a faulty brake light switch could also cause issues. This switch is usually located near the brake pedal.
To diagnose properly:
1. Test the bulbs: Ensure your bulbs are good.
2. Check fuses: Check the relevant fuses in the fuse box(es).
3. Use a multimeter: Check for continuity (a complete circuit) between the ground wire of the tail light and a known good ground point on the vehicle chassis. If there's no continuity, you have a grounding problem.
4. Visual Inspection: Carefully inspect the wiring harness for any damage, especially near the tail lights, where it might be exposed to the elements.
Instead of searching for a specific "brake light ground wire," focus on finding where the tail light ground is connected to the chassis. If you have a wiring diagram for your specific 1999 GMC Suburban, it will be very helpful. You can often find these diagrams online through repair manuals or forums dedicated to GM vehicles. A repair manual will be extremely valuable in diagnosing this sort of issue.
