Buzzing Alternator

[gofstbuick]

I was doing a compression test the other day and I noticed that with key on engine off, the alternator is buzzing. I then turned the ignition off and did a amp test (through the ground wire) and the meter pegged over 100. Any ideas what would cause this?

 

[David65]

Did the frequency of the buzz sound like 400Hz? That's the frequency at which the regulator is switching the field current on & off, it's normal. What range was the meter on when it pegged over 100? 100mA's? Were any lights on, interior, hood, etc? Sounds like a light was on.

David

 

[gofstbuick]

Sounds like a light was on.

David

Yup (underhood light still connected), disconnected wire and it drops to .15 miliamps
Thanks for the info. I did a diode test this afternoon and everything was normal