Bad alternator or? - Dodge Cummins Diesel Forum
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post #1 of 16 (permalink) Old 08-13-2019, 12:56 AM Thread Starter
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Bad alternator or?

Hey everyone. First post. This site has saved me enough money to buy a new truck years ago. I’m starting to pull my hair out with my latest issue. I have a 07 5.9 w/ 180000 miles and am the original owner. I rebuilt the a/c system two weeks ago and it runs great. Also ended up having to replace the fan clutch. Several days after installing the fan clutch I got a ‘check gauges light’ with a P2305 code. Tested the batteries and was down to 10.8v and nothing coming of the alternator. Bought a new alternator and still no voltage coming off it. I’ve been charging the batteries manually the last few days and driving it still without getting the low voltage light on. I tested some more things tonight and I’ve got power on both prongs of the alternator connector. Did I get a bad alternator from nap?

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post #2 of 16 (permalink) Old 08-13-2019, 10:26 AM
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With engine idling:
What's the voltage reading output at the back of alternator?
What's the reading on the passenger side battery positive post?
What's the reading on the driver side battery positive post?
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post #3 of 16 (permalink) Old 08-13-2019, 12:17 PM Thread Starter
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With engine idling:
What's the voltage reading output at the back of alternator?
What's the reading on the passenger side battery positive post?
What's the reading on the driver side battery positive post?
I have no reading on the be post. Getting a 1. On the multimeter.

Passenger side is 11.87v

Driver side is 11.86v
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post #4 of 16 (permalink) Old 08-13-2019, 12:32 PM
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Most likely blown fusible link in the wire from + AUX side batt to alternator post.
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post #5 of 16 (permalink) Old 08-13-2019, 01:29 PM
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Originally Posted by Kar6man View Post
I have no reading on the be post. Getting a 1. On the multimeter.

Passenger side is 11.87v

Driver side is 11.86v
That only tells that there is no charging juice coming to the batteries.
it doesn't meant that there is no charging juice output from alternator.
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post #6 of 16 (permalink) Old 08-13-2019, 01:33 PM
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Quote:
Originally Posted by steelhead1 View Post
Most likely blown fusible link in the wire from + AUX side batt to alternator post.
http://www.rambodybuilder.com/2007/d...gingsystem.pdf

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post #7 of 16 (permalink) Old 08-13-2019, 01:38 PM
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Can tell you more if the alternator output voltage is posted.

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post #8 of 16 (permalink) Old 08-13-2019, 02:21 PM
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Follow PWONGS directions. PWONG knows all. You'll have a fix in no time with him helping.

I would guess fusible link. Which may trend towards an alternator issue.

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post #9 of 16 (permalink) Old 08-13-2019, 04:52 PM Thread Starter
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Thanks for all the replies. It turned out to be the fusible link. Replaced it with 6 ga. cable and a 150 amp inline fuse and all seems to be functioning normally now. Thanks again.
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post #10 of 16 (permalink) Old 08-13-2019, 05:44 PM
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Quote:
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Can tell you more if the alternator output voltage is posted.
For those who are interested about the alternator output:

If the reading is the same as the passenger side battery positive post then the fusible link is good and there is no output from alternator.

If the reading is 30s something volt then the fusible link is open and the alternator is good.
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post #11 of 16 (permalink) Old 08-14-2019, 01:31 AM
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find out why the fusible link blew out from high overcurrent. check for short to block/chassis from the alternator to the battery, worn through or crushed insulation.
Or someone momentarily grounded the + AUX side batt post while motor running. Jump starting cable connection sequence can also screw the pooch on the fusible link.
Sparks flying is usually in indication someone has screwed up and the good smoke has escaped.

Very lucky ECU is not fried
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post #12 of 16 (permalink) Old 08-14-2019, 02:54 AM Thread Starter
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Quote:
Originally Posted by steelhead1 View Post
find out why the fusible link blew out from high overcurrent. check for short to block/chassis from the alternator to the battery, worn through or crushed insulation.
Or someone momentarily grounded the + AUX side batt post while motor running. Jump starting cable connection sequence can also screw the pooch on the fusible link.
Sparks flying is usually in indication someone has screwed up and the good smoke has escaped.

Very lucky ECU is not fried
I cut open the wire this afternoon looked like a corrosion issue about 3 inches off the battery terminal eye. When I tried to inspect it it broke clean off. I’ve got the parts to replace the fusible link to the grid heater as well. It looks to be in a similar condition.
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