Battery drain caused by alternator exciter plug - JeepForum.com
 
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post #1 of 10 Old 07-12-2020, 02:48 PM Thread Starter
Wassabi
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Battery drain caused by alternator exciter plug

Troubleshooting a parasitic battery drain. I found out I was getting a 4 amp drain from somewhere. I finally found when I unplug the exciter cable from the alternator the drain goes to 0. Anyone know how to troubleshoot this exciter cable? I attached a photo of the plug I detached from the alternator that was causing the drain when plugged in.

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post #2 of 10 Old 07-12-2020, 03:19 PM
jtec
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likely bad diodes in the Alt.

I see you have a DVOM - google 'how to check alt diodes' there will be some youtube tutorials to help - easy fast to check... let us know

next I would be checking at the regulator - external if applicable.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #3 of 10 Old 07-12-2020, 03:32 PM Thread Starter
Wassabi
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I did diode test by unplugging the exciter plug and the power cable at the rear of the alternator. I put positive lead of multimeter on alternator casing and read voltage and then reversed the leads. According to the you tube videos one of the readings will show about .500 and the other should be 0. Which tests to make sure voltage only goes in one direction which is the purpose of the diodes. And it seems ok.
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post #4 of 10 Old 07-12-2020, 03:38 PM Thread Starter
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Correction , red test lead on alternator casing and black test lead on rear of alternator where power cable was connected. Then reversed test.
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post #5 of 10 Old 07-12-2020, 03:40 PM
jtec
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what year jeep?

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #6 of 10 Old 07-12-2020, 03:48 PM Thread Starter
Wassabi
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1990 yj
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post #7 of 10 Old 07-12-2020, 03:49 PM Thread Starter
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4.2 6 cylinder
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post #8 of 10 Old 07-13-2020, 12:18 AM Thread Starter
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I think for a 1990 Jeep yj the voltage regulator is built into the alternator.
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post #9 of 10 Old 07-13-2020, 06:14 AM
fishadventure
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You can get an alternator shop to install a self-exciting module in most alternators.


I had to do that for a 1989 Grand Cherokee/AMC 360 I was working on that had a pesky battery drain.

It was cheap ($35 with labor?) and solved a 900mA I couldn’t find but unfortunately I got a lay-off notice before I could solve a remaining 65mA mystery.

[size=3]Shackles & D-rings are different things.
Cranking IS turning over
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post #10 of 10 Old 07-15-2020, 03:37 PM Thread Starter
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Looks like the voltage regulator in the alternator was bad. Replaced alternator and battery doesn’t drain anymore.
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