• Dead battery.
  • Dim lights.
  • Flickering gauges.

Any one of these symptoms can be a sign of a weak charging system. Your charging system is responsible for restoring the charge to your car battery after use and is tasked with providing power to your lights, audio system, and other electronics while your vehicle is running. Without your charging system in proper working order, you’ll eventually find yourself stranded…without lights…and without good tunes. Gasp.

To help you avoid such a situation, we’ve put together a basic guide to tracking down potential charging system issues.

(Image/Wayne Scraba)

Problem: Engine starts OK, but the battery does not stay charged.

Solution #1: Focus on your battery first. If your vehicle has stopped running, jumpstart the engine, remove the jumper cables as quickly as possible, and wait. If the vehicle keeps running after a period of time, there’s likely a problem with your battery. Take into account the outward appearance and age of the battery when deciding whether to replace it. Also, inspect your battery cables and make sure they are in good shape. Bad cables will not deliver the full current flow needed to operate properly.

Solution #2: If the battery won’t hold its charge and your engine stalls out, then it’s time to turn your attention to the alternator. Although your battery may have enough energy to get the engine fired up initially, it will eventually lose power if it is not being recharged by the alternator. Here are a few quick ways to pinpoint a bad alternator:

  1. Crank over the engine, turn on your vehicle’s lights, and observe. If they start bright and then slowly fade, your alternator might not be delivering the proper charge to operate your vehicle accessories.
  2. If your vehicle is already dead, jumpstart the battery and wait. If the alternator is bad, your car or truck will eventually die out again as the battery is not re-charged.
  3. Get a good-quality voltmeter or multimeter and test your battery’s state of charge. The voltmeter should read around 12.6 volts with the engine off and 14-15 volts when the engine is running. If voltage is below 13.5, there’s a good chance the alternator is not keeping up with your battery’s charging needs.

Solution #3: Check the alternator cables for abnormal wear, including cracking and fraying. Replace or tighten the cables as necessary.

See Also:
Ask Away: with Jeff Smith: When and How to Update the Charging System in a Classic Car
Monday Mailbag: Tracking Down Potential Charging System Issues

Problem: Engine cranks over slowly and lights dim excessively during process.

Solution: Slow or labored cranking is often the first sign of an undercharged battery. Use the tests above to determine the problem—battery or alternator.

Problem: Lights flare excessively as engine speed increases.

Solution: This is usually caused by an overcharged battery, which is typically the result of high alternator voltage. This can be caused by a short or ground in the rotor field winding within the alternator or a defective regulator.

Problem: Dim lights or lights that seem to fade as the car runs.

Solution #1: Since the alternator is responsible for supplying the auxiliary power to your lights and electrical components, start with the alternator and associated items. First, examine the wiring for damage or wear and replace as necessary. If everything looks good, move on to solution #2.

Solution #2: Turn on your vehicle and use a voltmeter to test your battery’s charge. If voltage is below 13.5, there’s a good chance the alternator is not keeping up with your battery’s charging needs and will need replaced. If voltage is around 13.5-15, turn your attention to your battery.

Solution #3: If the alternator is supplying proper voltage, chances are the problem lies with your battery.

Problem: Noisy alternator.

Solution #1: Check the alternator belt for wear or looseness. Replace or tighten as necessary, making sure the belt is properly aligned on the pulley. Improperly aligned alternator belts will often make a whining sound.

Solution #2: Check for bent pulley flanges that may cause the belt to run out of alignment.

Solution #3: Make sure the alternator is mounted securely so there is not excess movement.

Solution #4: Perhaps your alternator has seen better days and is on the verge of failure. Once you’ve gone through solutions 1-3, you may need to consider replacing the entire unit if the noise persists.

Problem: The charge indicator light flickers while driving.

Solution: At the very least, you likely have a loose alternator belt or bad wiring connection. Start by inspecting the alternator belt for wear and tightening it as needed. Also look for improper wiring connections. If one of these areas isn’t the culprit, you likely have a faulty alternator or regulator, which will need replaced.

Problem: The charge indicator light comes on while driving.

Solution #1: Again, this could be a sign of a bad alternator or defective regulator. But first, rule out some other possible causes, including a loose or worn alternator belt. Inspect and replace an abnormally worn belt and tighten a loose belt.

Solution #2: Check for wiring issues. The two most likely causes are a defective field-circuit ground or a bad light circuit wire or connector.

Solution #3: Once you’ve eliminated the belts and wiring as possible problems, you’ll want to test your alternator for proper operation.

Author: David Fuller

David Fuller is OnAllCylinders' managing editor. During his 20-year career in the auto industry, he has covered a variety of races, shows, and industry events and has authored articles for multiple magazines. He has also partnered with mainstream and trade publications on a wide range of editorial projects. In 2012, he helped establish OnAllCylinders, where he enjoys covering all facets of hot rodding and racing.