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How to Troubleshoot a Harley Alternator

by Jim Murkot Sr.

The charging system on a Harley-Davidson motorcycle consists of the battery, the voltage regulator and the alternator. The alternator, in turn, is made up of the rotor and the stator. Located within the primary chaincase on the left side of the engine, the alternator is difficult to visually inspect. Fortunately, it is quite simple to troubleshoot. The alternator's performance may be tested with a digital multimeter for both a grounded stator as well as correct AC output.

Grounded Stator

Step 1

Harley Crankcase

Turn off the motorcycle's ignition. Disconnect the plug leading from the voltage regulator to the crankcase.

Step 2

Digital Multimeter

Measure the resistance between one hole on the stator plug and a known ground point on the motorcycle. Ensure that the meter is reading resistance on the Rx1 setting.

Step 3

Verify that there is no continuity between the stator plug and ground. Any reading other than zero means that your stator is bad.

Measure the resistance in between both holes on the stator plug. The meter should indicate 0.1 to 0.2 ohms across the socket. A lower resistance means that the stator is bad.

AC Output

Step 1

Start the motorcycle. Leave the plug from the voltage regulator to the crankcase disconnected. Run the engine at approximately 2,000 RPM. Measure the AC output from the stator plug with the digital multimeter set to read "Volts AC."

Step 2

Check that the reading is between 32 to 40 volts AC.

Determine that the alternator is bad and must be replaced if the reading falls below 32 volts AC.

Warning

  • Remove all watches and rings when working around electricity. While a motorcycle battery may be small, it contains sufficient power to cause a serious burn.

Items you will need

  • Digital multimeter

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