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One wire alternator

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Category: Allis Chalmers
Forum Name: Farm Equipment
Forum Description: everything about Allis-Chalmers farm equipment
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=170327
Printed Date: 22 Aug 2025 at 8:16pm
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Topic: One wire alternator
Posted By: 1947WC
Subject: One wire alternator
Date Posted: 20 Apr 2020 at 1:41pm
Is there any way to test a 1 wire alternator with a test light it's a positive ground.



Replies:
Posted By: Jim.ME
Date Posted: 20 Apr 2020 at 3:36pm
I am guessing you are talking about checking alternator output. About the only thing I can see a test light will tell you is there is power at the alternator output stud, which it should have at all times on a one wire alternator. You need a voltmeter to see if the voltage changes when it is running. Positive or negative ground makes no difference in that. I have to ask this, Are you sure it is actually a positive ground alternator?


Posted By: Dakota Dave
Date Posted: 20 Apr 2020 at 5:57pm
Take it off and take in and have tested at the auto parts store. If your alternator has been hooked up POS ground your going to need a new one any way. The diodes are blown and it'll have no output. There are specitly shops that will make a POS ground alternator but they are very expensive. Negative ground became the world standard even before 12 volts became the standard voltage.


Posted By: DiyDave
Date Posted: 20 Apr 2020 at 5:59pm
Check with a volt meter, at battery. volts running, vs volts not running...Hug

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Posted By: 1947WC
Date Posted: 20 Apr 2020 at 9:01pm
Thanks Jim.ME


Posted By: 1947WC
Date Posted: 20 Apr 2020 at 9:08pm
Thanks Diy.Dave


Posted By: 1947WC
Date Posted: 20 Apr 2020 at 9:13pm
Thanks Dakota.Dave


Posted By: Adam Stratton
Date Posted: 20 Apr 2020 at 9:24pm
Touch something metal to the bearing on the back of the alternator. If it magnetized, it is charging, if not it isnt


Posted By: 1947WC
Date Posted: 22 Apr 2020 at 1:09pm
I'll try that. Thanks Adam.


Posted By: jaybmiller
Date Posted: 22 Apr 2020 at 1:16pm
if, IF, the test light was an LED, then yes.....though everyone has a voltmeter. Just be sure the test leads are in properly(red2red,bl2blk) !!!
99.44% of all alternators are NEG ground BTW....


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