How do you know when the alternator is going on your car?

If the voltage level is low or the battery is not getting an adequate charge, you may have an alternator problem. Unfortunately, there are no single lights, gauges or other indicators that you can look at to see for certain that it's the alternator. The best way to check the condition of an alternator is to take the vehicle to an auto parts retailer, such as Auto Zone or whatever their competition is in your area. They'll generally test your entire charging system and tell you what's wrong. They do this in hopes that you'll buy the replacment parts from them, so they don't charge for that service. If you don't really want to take it anywhere, see if you can get a volt meter. Test the battery voltage when the vehicle is not running. With the meter turned on, just hold the point of the red wire against the positive battery terminal and the point of the black wire against the negative battery terminal. The battery should show very close to 12 Volts DC. Don't use the AC scale, or the amps or any other feature of the meter, since it is quite possible that doing so would destroy the meter. The battery terminal will not harm YOU. It's only 12 volts, not even enough to feel. If the voltage is low, for example around 10 volts or less, you may need to charge the battery or get a battery boost from another vehicle before the car will even start. Once the car is started, make sure all other charging devices and vehicles are disconnected from the vehicle you're testing. Connect the meter to the battery again and find out what the voltage is when the engine is running. Have a friend bring the engine up just a little from idle when you test the voltage. You should get about 13.5 Volts DC, but your vehicle may be a little different, and the meter may be calibrated a little off as well, but if it's anywhere from 13 to 14 volts, the alternator is probably working ok. Turn on the lights, rear window defroster, AC and wipers to see if the voltage goes down. No matter what accessories you turn on, the alternator should be able to keep the voltage constant. If not, it's probably a faulty alternator.