Alternator going bad?

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Gremlinsteve

Master Mechanic
Mar 6, 2018
345
426
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Reason I'm asking is I just replaced my alternator
It started showing a discharge most of the time on the factory gauge

So I replaced it and I'm showing a discharge still
At idle it's dropping down to 8-9 volts indicated
And at 2500 rpm cruise it shows a 12-12.5 area tops

Measured at battery terminals at idle I'm seeing 12.22 volts

Is the new alternator bad also?
 

Streetbu

Know it all, that doesn't
Supporting Member
May 22, 2011
3,721
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Central NY
Sounds like it. You should see 14.3v all the time...
 
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melloelky

Comic Book Super Hero
Oct 22, 2017
4,136
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mass
With the engine running carefully take a screwdriver and place it on the back of the case.if the driver is strongly drawn towards the back it's charging.
 
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Zspoiler

Apprentice
Jun 3, 2018
85
55
18
Take it back f you are not satisfied with it.They can bench test them at the store.And if you still have issues,Then you know its not your altrenator.
 

565bbchevy

Geezer
Aug 8, 2011
9,590
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Michigan
I would do all of your testing with a volt meter and test from the output terminal off the back of the alternator and disregard anything your factory gauge tells you
 
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airboatgreg

Comic Book Super Hero
Oct 2, 2016
2,863
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What kind of car?
Alternator type?
gauges or idiot light
 
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airboatgreg

Comic Book Super Hero
Oct 2, 2016
2,863
3,112
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make sure you have 12volts to rear of alternator and to red wire that plugs into regulator. Brown wire is turn on so unplug 2 wire connector, start propulsion plant and see if you have 12 volts. With engine running see what your voltage is at the rear output, if it happens to be real high you have an open wire. Rare but something to think about.
If all good bad alternator.
 
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