You are driving to a gas station when your headlights start to dim. Your headlights are not completely broken, but they do tend to fluctuate in brightness. Even if the dimming is temporary and returns to normal brightness, it is best to examine the problem now in case your headlights fail completely when you are on the road. Try the following tips if your headlights dim while driving.
A common reason for intermittent headlight dimming is a bad alternator. But before you test the alternator, you must check that the battery can start the alternator. The battery is responsible for initially powering the alternator, but relies on the alternator to stay charged.
Checking the battery
1. Turn off your car.
2. Put the red part of the voltmeter to the red battery terminal.
IMPORTANT: Do not let your skin touch the battery.
3. Do the same for the corresponding black parts of the voltmeter and battery terminal.
4. Test the battery. If it measures to be over 12.2 volts, then it can start the alternator.
Check the alternator
1. Disconnect the voltmeter.
2. Start your car.
3. Turn on the headlights.
4. Rev the engine to 2,000 RPM. This should cause the alternator to go into high gear.
5. Reconnect the voltmeter to the battery, being careful not to let the battery touch your skin.
6. Test the battery. If the voltage fluctuates between 13 and 14.5 volts, then your alternator is working properly. If the voltage stays the same or decreases, then you may need to fix or replace your alternator.
If you are not sure if the alternator needs to be fixed, see if your car shows other symptoms.
Symptoms of a bad alternator
Warning light comes on
In most modern cars, there is a warning light shaped like a battery on the dashboard. It can be marked by an “ALT,” which stands for alternator. Pay attention to this light because it can flicker on and off if the alternator is having problems.
Drivers report hearing a growling or whining noise when their alternators are failing. This is because the alternator pulley is not aligned with the accessory belt or because the pulley bearings are worn out.
Burning rubber/hot wire smell
The burning rubber smell indicates that the pulley is causing friction on the belt. The hot wire smell indicates the alternator is overworking the rotor and stator.
When in doubt, it is safest to have your car checked by a professional. TalkLocal can help you find local auto repair services in minutes and address the problem of dimming headlights before it gets worse.