* Loose or damaged wiring. Make sure that all of the wires connected to the alternator are properly secured and in good condition. If any of the wires are loose or damaged, they could be preventing the alternator from charging the battery properly.
* Bad alternator. Even though you just replaced the alternator, it's possible that the new one is defective. If the alternator is not working properly, it will not be able to charge the battery, and the check charging system light will come on.
* Problem with the battery. If the battery is not able to hold a charge, the alternator will not be able to charge it properly, and the check charging system light will come on.
* Problem with the voltage regulator. The voltage regulator controls the amount of voltage that the alternator produces. If the voltage regulator is not working properly, it could be causing the alternator to produce too much or too little voltage, which could damage the battery and cause the check charging system light to come on.
If you are not able to figure out the problem yourself, you should take your car to a mechanic to have it diagnosed.
