* Alternator Failure: This is the most common cause. The alternator is responsible for charging the battery while the engine is running. If it's failing, it won't replenish the battery's charge, leading to the light coming on. This could be due to a bad alternator itself, a faulty voltage regulator (often part of the alternator), or bad wiring/connections to the alternator.
* Bad Battery: While less likely to directly cause the light to come on (it's more of a symptom), a severely degraded battery might not accept a charge properly, causing the charging system to struggle and trigger the light.
* Bad Battery Cables or Connections: Corrosion or loose connections on the battery terminals, or anywhere in the charging system's wiring, can prevent proper current flow and trigger the warning light.
* Wiring Problems: A break or short in the wiring between the alternator, battery, and the warning light itself can also cause the light to illuminate.
* Voltage Regulator Issues (if separate from alternator): Some older vehicles have a separate voltage regulator. A malfunctioning regulator won't properly control the alternator's output, leading to overcharging or undercharging and triggering the light.
To diagnose the problem, you'll likely need a multimeter to check the battery voltage (with the engine off and on), and the alternator output voltage (with the engine running). You should also visually inspect the battery terminals and cables for corrosion and tightness. If you're not comfortable doing this yourself, take it to a mechanic for proper diagnosis and repair.
