Signs that the alternator is going bad include dim lights, odd smells, a weak or dead battery, unusual sounds, or a warning light. If the alternator goes out completely, expensive repairs are often the result, but these signs give the owner time to replace it before failure.
When the headlights do not provide their normal brightness, or the lights on the dashboard flicker or stay dim, the alternator may be waning. Its job is to provide the power for all of the car's electronic accessories in addition to the ignition and the starter. In addition to dim lights, slow performance from power windows or power seats also indicates the possibility of a faulty alternator.
Most modern models have a warning light on the dashboard indicating alternator trouble. This is either shaped like a battery or consists of the letters ALT for alternator or GEN for generator. However, this light sometimes only activates when the alternator is bad and the driver is using multiple electric accessories at once.
If the battery is weak but providing a charge to it does not restore it to life, the problem may be the alternator. A fully charged battery should start the car easily, so if the car doesn't start after a charge, the alternator is likely the issue. If the engine gives of a smell of rubber, the belts that work with the alternator may be slipping, keeping alternator output low. A whining or grinding sound from the engine sometimes comes from worn out bearings in the alternator. The mounting bushings may also be the problem. In general, people replace the whole alternator assembly rather than just parts of the unit.