The Ford Barn

dshebuski · 06-02-2010, 12:38 AM

I have an alternator on my 31 coupe. The ammeter needle jumps from -20 to+20 continously as i drive at any speed. I have checked for a loose wire and also have the proper belt tension. Any suggestions???DWS

Ted · 06-02-2010, 02:59 AM

Does it have a good ground connection?

Barry B./ Ma. · 06-02-2010, 05:05 AM

If all the connections are tight and the grounds are good I would suspect the alternator. I've had new alternators before that had bad regulators but usually the just overcharge.Could be a bad regulator circuit in the alternator but with it pulling down 20 amps I would first suspect a short somewhere. Disconnect the lighting circuit wire from the alternator first and try it again to verify that it's not in that circuit then check the connections on your ammeter.

Tom Wesenberg · 06-02-2010, 05:36 AM

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In addition to what Barry mentioned also check the terminal box for a bad connection. With the car off, turn on the headlights. Set your multimeter to measure the lowest DC volts and connect the 2 meter leads to the 2 terminal box wing nuts. You should measure no volts. If the meter measure some voltage or if either stud gets warm it indicates a bad connection at the studs or the amp guage.

As Barry mentioned, I've also seen alternators with bad voltage regulators.

06-02-2010, 12:38 AM	#1
dshebuski Junior Member Join Date: May 2010 Location: manitowish waters wi. Posts: 19	ammeter jumping I have an alternator on my 31 coupe. The ammeter needle jumps from -20 to+20 continously as i drive at any speed. I have checked for a loose wire and also have the proper belt tension. Any suggestions???DWS

06-02-2010, 02:59 AM	#2
Ted Member Join Date: May 2010 Location: W. Mich. Posts: 47	Re: ammeter jumping Does it have a good ground connection?

06-02-2010, 05:05 AM	#3
Barry B./ Ma. Senior Member Join Date: May 2010 Location: Southbridge, Ma. Posts: 1,614	Re: ammeter jumping If all the connections are tight and the grounds are good I would suspect the alternator. I've had new alternators before that had bad regulators but usually the just overcharge.Could be a bad regulator circuit in the alternator but with it pulling down 20 amps I would first suspect a short somewhere. Disconnect the lighting circuit wire from the alternator first and try it again to verify that it's not in that circuit then check the connections on your ammeter.

06-02-2010, 05:36 AM	#4
Tom Wesenberg Senior Member Join Date: May 2010 Location: Mpls, MN Posts: 27,582	Re: ammeter jumping Sponsored Links (Register now to hide all advertisements) In addition to what Barry mentioned also check the terminal box for a bad connection. With the car off, turn on the headlights. Set your multimeter to measure the lowest DC volts and connect the 2 meter leads to the 2 terminal box wing nuts. You should measure no volts. If the meter measure some voltage or if either stud gets warm it indicates a bad connection at the studs or the amp guage. As Barry mentioned, I've also seen alternators with bad voltage regulators.