* Faulty Passlock System: The Passlock system is a common anti-theft feature in GM vehicles from that era. A malfunctioning Passlock system (often involving the ignition switch, wiring, or the Passlock module itself) can trigger the anti-theft light and prevent the car from starting or running properly, even while driving. This is the most likely culprit.
* Low Battery Voltage: A low battery can sometimes interfere with various electrical systems, including the anti-theft system. This is less likely to cause a *constant* light, but a fluctuating voltage could trigger it intermittently.
* Faulty Wiring: Damaged or corroded wiring in the anti-theft system's circuitry can cause erratic behavior, including the light illuminating. This could be anywhere in the system's wiring harness.
* Security System Malfunction: While less common, a problem with the actual security system components (sensors, etc.) could also be the cause. This might require professional diagnostics.
* Aftermarket Alarm System: If you have an aftermarket alarm or security system installed, it might be the source of the problem. Its wiring or components could be interfering with the factory system.
What to do:
1. Check the battery: Have the battery's voltage tested. A low or weak battery can cause all sorts of electrical gremlins.
2. Try to restart the car: If the car stalls or experiences running issues when the light comes on, the Passlock system is a prime suspect.
3. Check for any unusual noises or behavior: Listen carefully for clicking sounds from the steering column (near the ignition switch) which often signals Passlock issues.
4. Professional diagnosis: Because pinpointing the exact problem in an anti-theft system often requires specialized tools and knowledge, it's best to take the car to a qualified mechanic or a shop specializing in older GM vehicles. They can use a scan tool to check for diagnostic trouble codes (DTCs) that can help narrow down the source of the problem.
Ignoring a persistent anti-theft light is not recommended. It could eventually lead to the car becoming undrivable. Professional help is generally the most efficient way to resolve this type of issue.
