1. Fuses: This is the easiest and cheapest thing to check first. Your owner's manual will show you the fuse box location and diagram. Locate the fuse(s) for the headlights (often labeled "Headlights," "Headlamp," or a similar designation) and check for a blown fuse. A blown fuse will appear broken or have a melted filament. Replace with a fuse of the same amperage.
2. Bulbs: Headlight bulbs burn out over time. Check both low and high beam bulbs. This involves accessing the headlight assemblies (often from the engine compartment or from behind the headlight housing, depending on the trim level). Replace with the correct type and wattage bulb.
3. Headlight Switch: The switch itself could be faulty. It might be internally broken or have corroded contacts. This is less common but possible. Testing the switch requires some electrical knowledge or a multimeter.
4. Wiring Issues: Damaged or corroded wiring in the headlight circuit can interrupt the flow of electricity. Look for frayed wires, loose connections, or corrosion, especially near the headlight bulbs, connectors, and the switch. Repair or replace any damaged wiring.
5. Relays: Headlights often use relays to switch the higher current needed for the bulbs. A faulty relay can prevent the headlights from turning on. Relays are relatively inexpensive and easy to replace, once you locate the correct one (usually in a fuse box or under the hood).
6. Multi-Function Switch (often called the turn signal switch): This switch controls the headlights, turn signals, wipers, and sometimes other functions. If it's faulty, it could affect the headlights. Replacement is usually more involved and may require some mechanical knowledge.
7. Body Control Module (BCM): In some cases, a faulty BCM can cause electrical problems, including headlight failure. This is a less common cause and usually requires a professional diagnosis with specialized tools.
8. Grounding Issues: A poor ground connection can prevent electricity from reaching the headlights. Check the ground points for corrosion or loose connections.
Troubleshooting Steps:
1. Start with the fuses: This is the quickest and easiest check.
2. Check the bulbs: A burned-out bulb is a very common cause.
3. Inspect the wiring: Look for any obvious damage or corrosion.
4. Check the headlight switch: Try wiggling it gently while someone checks if the headlights work.
5. If none of the above works, it may be time to consult a mechanic: They have the tools and expertise to diagnose more complex electrical problems.
Remember to always disconnect the battery's negative terminal before working on any electrical components in your vehicle to prevent accidental shocks or short circuits. Consult your owner's manual for specific instructions and diagrams related to your 1999 GMC Suburban.
