1. Check the Switch:
* Manual Switch: If your Cavalier has a manual dome light switch (a pull-string or a rocker switch on the overhead console), the switch may be faulty. Try gently jiggling the switch. If the light flickers or goes out momentarily, the switch is likely the culprit and needs replacing. You can usually purchase a replacement at an auto parts store.
* Automatic Switch (if equipped): Some Cavaliers had automatic dome lights that turned on when the doors opened. If this is the case, check the door switches. A faulty door switch can keep the light on even when the door is closed. Test each door switch individually. Open and close each door and see if the light reacts appropriately. A faulty switch might be stuck "on." You'll likely need to replace the faulty door switch (they are often relatively inexpensive and easy to replace).
2. Inspect the Wiring:
* Overhead Console: Carefully remove the overhead console (usually held in place by clips). Inspect the wiring harness connected to the dome light switch and the dome light itself for any frayed wires, broken connections, or loose terminals. Look for any signs of corrosion or damage. Repair or replace any damaged wires.
* Door Switches (if applicable): If you're suspecting a door switch issue, you'll need to trace the wiring from each door switch back to the dome light circuit. Again, look for damage or loose connections. Repair or replace as needed.
* Ground Connection: A poor ground connection can cause the light to stay on. Check the ground wire connected to the dome light fixture itself – make sure it's clean, secure, and properly grounded to the vehicle's body.
3. Check the Dome Light Bulb:
While less likely to be the cause of the light *staying* on, a faulty bulb can sometimes cause unusual behavior in the circuit. Try replacing the bulb with a new one.
4. Fuse Check (Less Likely): While less common, a short circuit in the dome light circuit could cause a fuse to blow, but the light could also stay on if the fuse was bypassed or simply didn't blow. Check the fuse box (usually under the hood or dashboard) and check the fuse related to the dome light circuit.
Important Considerations:
* Safety First: Disconnect the negative terminal of your battery before working with any electrical components to prevent accidental short circuits.
* Wiring Diagrams: A wiring diagram specific to your 1999 Chevy Cavalier will be invaluable in tracing the circuit. You can often find these online (through repair manuals or forums dedicated to the Cavalier).
* Professional Help: If you are not comfortable working with car electrical systems, take your car to a qualified mechanic.
By systematically checking these areas, you should be able to identify and fix the problem causing your 1999 Chevy Cavalier's interior light to stay on. Remember to always prioritize safety when working with car electrical systems.
