1. Fuses: This is the first and easiest thing to check. Your owner's manual will show you the fuse box location and diagram. Check the fuses related to headlights and brake lights (they'll be clearly labeled). Replace any blown fuses with the correct amperage. *Don't* just replace a blown fuse with a higher amperage fuse – that's a fire hazard.
2. Bulbs: Next, visually inspect the headlights and brake light bulbs themselves. Are they burnt out? Remove and carefully inspect them. If they are burned out, replace them with the correct type and wattage.
3. Multi-Function Switch (also called turn signal switch): This switch controls several functions, including headlights, turn signals, and often the high beams. A faulty multi-function switch is a common cause of headlight problems. It's more involved to replace, but if the other checks come up negative, it's a strong suspect.
4. Brake Light Switch: This switch is located near the brake pedal and activates the brake lights when you press the pedal. It's a relatively inexpensive part and relatively easy to replace. If you test the brake lights with the ignition on and someone presses the brake pedal, and nothing happens, it's likely this switch. You can test it with a multimeter to see if it's closing the circuit when the pedal is depressed.
5. Wiring and Connectors: Look for any damaged, corroded, or loose wiring, especially around the headlights, taillights, and fuse box. Pay attention to the connectors. Corrosion can prevent a good electrical connection. Clean any corroded connectors with a wire brush and electrical contact cleaner.
6. Headlight Switch: The headlight switch itself could be faulty. This is less common than the multi-function switch but still possible.
7. Body Control Module (BCM) or other electrical components: In some cases, a problem with the BCM or other electrical modules could be the culprit. This is less likely, but possible. Diagnosing this requires more advanced diagnostic tools.
8. Grounding Issues: A poor ground connection can prevent the lights from working. Check the grounding points for the headlight and taillight circuits. They're usually metal points bolted to the chassis.
Troubleshooting Steps:
1. Start with the fuses. This is the quickest and easiest check.
2. Check the bulbs. Replace any burnt-out bulbs.
3. Test the brake light switch.
4. Inspect the wiring and connectors. Look for corrosion or damage.
5. If none of the above work, it may require professional help. A mechanic can use diagnostic tools to pinpoint the exact problem.
Remember safety first! Work on your car in a well-lit area and disconnect the battery negative terminal before working on any electrical components. If you're not comfortable working on car electrical systems, take it to a qualified mechanic.
