How to Tell If Alternator Brushes Are Bad
- 1). Check that you have no loose clothing or jewelry that could become caught up in the engine before checking to tell if your alternator brushes are bad. Many serious accidents occur as a result of clothing becoming caught in engines while they are running.
- 2). Open your car hood and secure in place. Start your car and let the engine idle for a while.
- 3). Use your voltmeter to check if your brushes are bad. Connect the negative wire from the voltmeter to the negative terminal of the battery using the spring clip on the end of the wire to secure in place.
- 4). Connect the positive wire from your voltmeter to the positive terminal of your battery. Secure in place using the spring clip on the end of the wire.
- 5). Check the readout from the dial on your voltmeter. With the engine idling and electrical equipment turned off, it should read 14.2-volts. If the volts are less than 13 you may have bad brushes.
- 6). Turn on electrical equipment such as lights and other devices that use a reasonable amount of electricity. Check the voltage on the voltmeter. It should remain at around 13-volts. If it falls below 12-volts your, brushes may be bad.
- 7). Get a friend to sit in the car and increase the engine speed to just above 2,000 RPM. Look at the voltmeter to see if it displays an increase in volts. Your voltmeter should display about 14 volts--maybe a little more if the battery is low. If there is little or no increase in voltage your brushes may be bad.
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