altenator question
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Joined: Feb 2004
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From: Missouri
altenator question
I'm having trouble with the charging system on my 75 f250. I took the alternator to the local parts store to have it checked and they said it was fine. So I replaced the regulator and still it is not charging. I read my shop manual and it said to check the field terminal with an ohm meter and it is shorted to ground is this normal or are the guys at the parts store wrong and the alternator needs to be replaced? From what I have been reading and kind of understand is that the field terminal accepts a variable voltage from the regulator and tells the alternator how much charge to put out.
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Joined: Jan 2001
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From: Virginia
I am not exactly sure the resistance value of the field coil. It might be pretty low though, so your meter needs to be on the rx1 scale to make sure it doesn't give you a false reading.
Their machine should have picked up a shorted field. If you want to do your own test, put your voltmeter on the battery. Take the field wire off the alt and hook a short piece of wire directly to the field terminal.
Start the engine, and while monitoring the battery voltage with your meter, touch the field wire directly to the + battery post. This will throw the alternator wide open, and you should see the voltage jump up on the meter, and you will probably hear the alternator start whining.
Their machine should have picked up a shorted field. If you want to do your own test, put your voltmeter on the battery. Take the field wire off the alt and hook a short piece of wire directly to the field terminal.
Start the engine, and while monitoring the battery voltage with your meter, touch the field wire directly to the + battery post. This will throw the alternator wide open, and you should see the voltage jump up on the meter, and you will probably hear the alternator start whining.
