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Battery charging issues. Alternator or wiring?

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Old 10-27-2015, 11:09 AM
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Battery charging issues. Alternator or wiring?

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Old 04-12-2012, 04:27 PM
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Canary94GT
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Default Solved: Battery charging issues. Alternator or wiring?

I am having some issues with my battery charging in my 1994 GT and need it fixed ASAP because it's my daily driver.

My 5-year old battery died slowly while driving about a week ago (eventually wouldn't start), and I didn't bother getting it recharged and just bought a new battery.

Well now I notice my battery isn't getting charged all the time(which explains the dead old battery). When I start the car, the battery gauge is usually about 3/4th full, and the battery reads 15V. After I drive for a while, the gauge sometimes goes down to about 1/3rd full and the battery reads only around 11.88-12V with the car on. It appears to me the battery is not getting charged at that point.

Usually this transition from 3/4th to 1/3rd on the gauge happens rapidly when driving (one second 3/4th, next second 1/3rd). I have noticed it happen a couple times while at a stop light when the electric fan kicked on, but sometimes it happens when driving or starts out at 1/3rd when I start the car.

I just had the alternator tested at both O'Reilly's and AutoZone and it passed at both. But I realize they're not testing it for long.. only about 15-30 seconds. The AutoZone guy told me it might be the alternator giving out when it's hot.

Any ideas on what this could be? The alternator, the volt. regulator, or the wiring? Also, I'm a noob when it comes to electrical - are there any easy resistance/voltage tests I can do on the wiring?

Thank you

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Old 04-12-2012, 04:35 PM
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Heat creates resistance, resistance lowers voltage. Could be the alternator or the wiring. Wiring is usually well protected from these things via routing and sheathing, so best bet would be the alt. Do an ohm check on the charging wire just to be sure. Just had this happen to me on a customers altima, I'd get 14.4v when cold but once it gets hot, it fluctuated badly. Need a high speed meter to see it.
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Old 04-14-2012, 11:50 AM
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start simple and double check the motor/body grounds. Should b on the pass side on the back/bottom of the motor there is a stainless strap that goes between the two.
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Old 04-14-2012, 05:20 PM
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I've checked several wires for resistance and voltage, all seem to be okay.

I learned about a way to test the voltage regulator, which is to utilize the "ground here to test" bolt on the voltage regulator. Supposedly if you ground that bolt while the engine is running and the car starts charging, then the regulator is bad.

I grounded the bolt and it started charging.

Does anyone think I should replace the regulator ($70) or replace the alternator for a rebuilt one ($170)? I'm a jobless college student, so I need to conserve as much money as possible. But I'm wondering if I should rebuild the alternator at 83,000 miles?

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Old 04-14-2012, 07:02 PM
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It's up to you. Mileage doesn't matter so much for alternators, they get worn down from atmospheric elements. Don't forget you have a lot of scrapyard options too, those 3g alt's are in a lot of different cars.
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Old 04-14-2012, 07:15 PM
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if I am not mistaken there is a small portion of the cars voltage regulator that is behind the dash on the drivers side that is known to go out, and be hard to find to replace as well. It has not gone out on mine yet so I am not for sure unfortunatly.
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Old 04-14-2012, 09:12 PM
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Eureka!

I took the alternator off and took it to O'reillys to have them test it again. It FAILED this time! At that point, I decided to bite the bullet and buy the regulator + new brushes. Installed them using this awesome little guide, slapped the alternator back on and it was charging

Thanks for your help!
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Old 04-15-2012, 09:51 AM
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good to hear - just curious, you running under drive pullies?
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Old 04-15-2012, 10:57 AM
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No, it's all stock as far as the engine compartment goes.

Ah, it's such a relief not having to worry how I'm going to get to school next week.
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