Alternator Test and Replacement
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5th Wheeling
Joined: Mar 2021
Posts: 39
Likes: 4
Alternator Test and Replacement
Had the battery light turn on while driving home and noticed the dash voltage "gauge" drop to about 10v (needle over the letter N). Sure enough, at home while running, with the multimeter, tested batteries and was 11.9 on both. Removed both and Charged batteries (Interstate 850cca dated NOV2017) back to 12.6V. Checked battery CCA with meter and one is 742CCA SOH 87% and other is 728CCA SOH87% The 728CCA was the passenger battery. Reinstalled both batteries with the 748 in the pass side and 728 on driver side now.
While off, checked at Alt B+ and reading same as battery V. Checked red wire resistance from Battery to Alt and 0.5V.
While off, tested the exciter wire (light green) at the alternator with key on only and was getting 12v there. Also checked Diode with Multimeter and had 820 with red lead on case and black lead on Alt B+. With Black lead on case and Red lead on Alt B+, read 0. So Diode ok?
Turned key on, battery light on, truck started... waited for GPR to turn off, and still reading 12.6 at the battery.
So, safe to say ALT is bad or do I need to run other tests?
Thanks in advance.
While off, checked at Alt B+ and reading same as battery V. Checked red wire resistance from Battery to Alt and 0.5V.
While off, tested the exciter wire (light green) at the alternator with key on only and was getting 12v there. Also checked Diode with Multimeter and had 820 with red lead on case and black lead on Alt B+. With Black lead on case and Red lead on Alt B+, read 0. So Diode ok?
Turned key on, battery light on, truck started... waited for GPR to turn off, and still reading 12.6 at the battery.
So, safe to say ALT is bad or do I need to run other tests?
Thanks in advance.
Hotshot
Joined: Oct 2003
Posts: 17,799
Likes: 103
From: Ashland City, TN
I forget what wire it is, but there is one associated with the alternator that will give you funky readings because the connector becomes loose.
Somebody else will have to remember, I just remember they use like 1 strand of wire and it will connect up or some crap. I think its the little loose one on the top that's grey.
Hard to really know much on alternators though unless you load test them. They can put out the voltage sometimes but not provide a good load.
Somebody else will have to remember, I just remember they use like 1 strand of wire and it will connect up or some crap. I think its the little loose one on the top that's grey.
Hard to really know much on alternators though unless you load test them. They can put out the voltage sometimes but not provide a good load.
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5th Wheeling
Joined: Mar 2021
Posts: 39
Likes: 4
After checking all voltage at the Alt and back to the battery, i removed belt and hand spun the alternator, it sounded like a rusted bearing...
I replaced it with a Ultima New Alternator and voila, started and charging now.
So it was the alternator, but glad I learned a bit about the charging system.
I replaced it with a Ultima New Alternator and voila, started and charging now.
So it was the alternator, but glad I learned a bit about the charging system.
Hotshot
Joined: Oct 2003
Posts: 17,799
Likes: 103
From: Ashland City, TN
After checking all voltage at the Alt and back to the battery, i removed belt and hand spun the alternator, it sounded like a rusted bearing...
I replaced it with a Ultima New Alternator and voila, started and charging now.
So it was the alternator, but glad I learned a bit about the charging system.
I replaced it with a Ultima New Alternator and voila, started and charging now.
So it was the alternator, but glad I learned a bit about the charging system.
Thread Starter
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5th Wheeling
Joined: Mar 2021
Posts: 39
Likes: 4
It wasnt broken, but noticed it was looking pretty worn. Now that I know it was the alternator, gonna replace that pigtail.
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5th Wheeling
Joined: Mar 2021
Posts: 39
Likes: 4
With that said, gonna run a 2/0 new wire with a 200a external fuse straight from the alternator to the battery. Just picked up a lug crimping tool and 1/0-4/0 copper wire lugs to clean up the grounds and + cables at the battery.
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Mountain Pass
Joined: Jun 2009
Posts: 197
Likes: 10
I just went thru similar with the 215a alternator, changing that was a chore, you have to take one of the serpentine pulleys off as the tensioner won't release far enough to get the belt off.
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Hotshot
Joined: Oct 2003
Posts: 17,799
Likes: 103
From: Ashland City, TN
Sounds like your tensioner is bad. i got oogles of room for taking the belt off.
Mountain Pass
Joined: Jun 2009
Posts: 197
Likes: 10
The 215a alt has a different bracket & serp belt, special for the ambulance package. I thought the tensioner bad too and bought a new one, I left the original one on it, I preferred the original steel pulleys over the plastic. Its no big deal once I figured out what to do.
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