Checking Alternator
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Checking Alternator
The lights and instrument panel in my 1983 F100 IL6 dim when I am shifting. I measured the voltage on the battery at 12.1 V when the engine is off and 13 V when running.
I disconnected the field wire from the external voltage regulator and took a reading of 1 volt while the engine was running.
Is that the proper way to check the alternator output? What should be the output of the field wire? Do the dimming lights while shifting point to a dying alternator? The temperature gauge goes all the way to the right when the lights are on (even though the engine is not hot) – is this related to the alternator?
Many thanks for any help.
I disconnected the field wire from the external voltage regulator and took a reading of 1 volt while the engine was running.
Is that the proper way to check the alternator output? What should be the output of the field wire? Do the dimming lights while shifting point to a dying alternator? The temperature gauge goes all the way to the right when the lights are on (even though the engine is not hot) – is this related to the alternator?
Many thanks for any help.
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From: Virginia
Check the condition of the alt belt, and the tension. 13v means it is charging some. Take the battery positive cable off, and then take the other end that goes to the starter relay off, and clean all the connections and wire ends.
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Thanks for responding Dave. I looked at the connections and they look clean. I misstated something in my initial post. The black wire running from the alternator is attached to the starter relay on the same side as the red battery wire. Is this correct?
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From: Virginia
Yes. And that's the connection I was thinking may have a problem. That is the main connection where the output of the alt feeds the battery, as well as the rest of the truck. Besides the alt wire, you should have some other wires there that have fusible links, which feed all the elec to the rest of the truck. Is your idle speed up to spec? And it is possible that a diode may be blown in the alt, reducing the output a little bit.
Also unplug the regulator plug and then plug it back in. Maybe something is not connected good there.
Also unplug the regulator plug and then plug it back in. Maybe something is not connected good there.
Last edited by Franklin2; Oct 3, 2003 at 01:06 PM.
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Take your measurements also with all the accessories on and the engine running. A battery is a storage device for starting the vehicle. The alternator should power the accessories without any drain to the battery. If the voltage from this test drops below the 12.1 that you started with, the alternator and/or regulator are bad. An alternator usually puts out between 13.5 and 14.5 volts. Although this is a 12V system, the alternator has to charge above that in order for the battery to maintain 12V afterwards. Sounds like the alternator is weak or the regulator is not kicking in soon enough before the battery drains down. Sometimes even a bad battery will show full voltage with no load applied, so you may want to test the voltage at the battery with the engine off, all accessories on.
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From: Minneapolis, MN
Re: Checking Alternator
I disconnected the field wire from the external voltage regulator and took a reading of 1 volt while the engine was running.
I measured the voltage on the battery at 12.1 V when the engine is off and 13 V when running.
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From: Close to Mr. Anderson
also check the cable crimps, that is a unseen problem, where the
cable is either crimped or soldered, corrosion gets on the wires
or they get loose, will cause a loss of current...good luck
cable is either crimped or soldered, corrosion gets on the wires
or they get loose, will cause a loss of current...good luck
