Some of the things to look for are no-starting and trouble starting, dimming lights and problems with stereo system output. If your car starts but stalls when you’re underway, your battery is probably not being recharged due to a faulty alternator. A squealing sound coming from the engine that gets louder when drains like the heater or sound system are on may be your alternator bearings.
Another telltale is turning the AM radio to a low number on the dial without music, then revving the engine. If you hear a whine or the sound goes fuzzy when you hit the gas, your alternator is probably failing.
If the vehicle won’t crank or start but the headlights are still working, look to problems with the starter or other parts of the engine.
If you have a check-engine or battery indicator light illuminated on your vehicle, it could indicate a problem with an automobile charging system, or if your vehicle gets a jump-start and immediately stops running, it could be an indication that the alternator is malfunctioning. It’s important to bring this into a professional for a proper diagnosis.