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koates · 09-22-2020, 09:34 PM

As stated above one diode may be faulty out of the six main diodes inside. That will create a phase inbalance which creates a whine. If an alternator is charging at a high rate it can also make a whine. You need to check the voltage at the main terminal with some revs up and this should read around 14 volts. Also check what amps it is charging. I suggest you take it to an auto electrical shop so that they can run it up in their test bench. They would also have a diode load tester that can test each individual diode. Regards, Kevin.

09-22-2020, 09:34 PM	#3
koates Senior Member Join Date: May 2010 Location: Melbourne Australia. Posts: 2,079	Re: 38 ford alternator As stated above one diode may be faulty out of the six main diodes inside. That will create a phase inbalance which creates a whine. If an alternator is charging at a high rate it can also make a whine. You need to check the voltage at the main terminal with some revs up and this should read around 14 volts. Also check what amps it is charging. I suggest you take it to an auto electrical shop so that they can run it up in their test bench. They would also have a diode load tester that can test each individual diode. Regards, Kevin.