Common Alternator Issues & Causes

The alternator is one of the most important parts of the electrical system of any vehicle, serving to supply electrical power which the battery stores and protecting the system from electrical surges. As such a crucial component, it is important to be able to identify issues early on. This article will explore some of the most common signs of alternator issues and their causes so you can more accurately determine the correct course of action when it comes to repairing your heavy-duty equipment’s electrical systems.

Headlight Issues

One of the most common issues you will find when your alternator begins to fail is with your headlights. This is usually the result of the alternator generating inconsistent voltage which leads to equipment such as headlights either under or over-performing. You may find your lights dimming or becoming extremely bright, or flickering between the two. This can happen alongside other electrical faults such as speedometers and tachometers performing inconsistently, indicating an alternator problem.

The exact issues you face is dependant on a number of factors, such as how far along your alternator is in its death cycle, and how the vehicle is programmed to distribute electricity when problems arise.

Unusual Sounds & Smells

Over time, the belt that turns the alternator’s pulley can become worn and may misalign itself. It is also possible for the bearings that spin the rotor shaft to become damaged. Either of these can lead to a persistent growling or whining noise.

Similarly, a faulty alternator may also result in unpleasant smells. An overheated alternator can be the result of too much electricity being pushed through the wiring, which can cause a smell similar to an electrical fire. On the other hand, if the pulley becomes misaligned it may start creating more friction on the rubber belt, leading to the smell of burning rubber.

Either smells or sounds may be indicative of alternator issues, and should be looked at as soon as possible to prevent further damage and get a replacement alternator if necessary. However, it may be difficult to discern whether the smell or noise is the result of your alternator, so you should look for other symptoms to help pinpoint the cause of the problem.

Stalling & Difficulty Starting

If your alternator is failing to charge your battery, you may experience issues starting the engine or regular stalling. This is because the power that starts your vehicle and keeps it running comes from the electricity stored in the battery, so if it is not being sufficiently charged by the alternator, it won’t have enough power to start and run your vehicle. This can lead the incorrect assumption that it is always an issue with the battery, but it could be the result of a failing alternator.

In fact, sometimes a seemingly dead or dying battery is not actually a failure of the battery itself, but instead the alternator not sufficiently charging it. And in those instances where the battery is the problem, this can put stress on the alternator over time which leads to it becoming damaged as well.

Unsurprisingly, it can be difficult to tell when any given electrical problem is the cause of your alternator, as many different sources may be the culprit. But if you are experiencing more than one of these key problems or other issues related to an underperforming alternator including electrical issues such as flickering or dim dashboard lights, it is best to get your alternator checked.


Modern machines have sophisticated engine and machine management systems. Look out for error odes that indicate electrical charging issues. For older machines monitor the ammeter and consult a trained electrical technician if you suspect an alternator problem.

If you do find your alternator is in need of replacing, we stock and supply electrical components for Caterpillar, Komatsu, and Cummins machinery including alternators, spark and glow plugs, and starter motors. For more information about maintaining the electrical systems of your heavy-duty equipment, contact us via telephone at 01604 491 133 or email us at  

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