Question about 1991 Nissan Sentra 2 Door

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Alternator not charging idiot light off

First, let me apologize for the long email. let me tell you what happened. last week, i drove 20 miles to meet 2 friends for lunch. it's hot here in manila, so the ac was on and so was the cd player. no untoward incident happened on my way. it was a simple pick up my friends, park the car, go to the resto, have lunch and lots of laughs.

after lunch the car started perfectly. i take my friends back to their offices (ac and cd player on) and it happens. about half a mile from my last drop off, i decide to have a smoke. lo and behold only the driver side window comes down the other 3 do not.(btw, the car is a 91 sentra, 4 dr, ga16de, manual tranny).

to me, this indicated a weak battery and the alternator not charging it properly. long story short, i pass this electrical/battey shop and they tell me the alternator is shot. i asked them, if the alternator is busted, WHY DIDN'T THE IDIOT LIGHT COME ON? i ran through a couple of alternators. the first one overcharged the batt and the second one didn't charge it. so i know for a fact that overcharging and undercharging lights up the batt idiot light.

but in this case, the battery goes dead and the idiot never indicates an undercharging problem. so i just ask him to charge the batt as i have another engagement. true enough, i go my meeting, and the battery just had enough power to get me home that night.

what could be wrong? i read a post in one forum, that given this, the problem is not the alternator.

i did the tests i found in search and here's addtional info.

1. i measured the altenator voltage by placing the red probe of my voltmeter to the alternator's ''batt'' post and the black probe of the voltmeter to the alt's ground post. i got 12.1volts while the engine was running.

2. i tested continuity of the wire form the alt's batt post to the + battery connector. and this checks out ok.

3. after confirming continuity, i put back the battery connector to its place BUT left the alternator battery wire unconnected and started the car.

the car started fine but noticed 2 thingsw.

a.) when i turned on the ignition but not started the car yet, the batt idiot light did not come on.

b.) when the engine ran, the batt idiot light stayed off.

do these tests help? i hope you can assist me. i would like to know what other tests i can do the determine what's wrong. and if it's the alternator, what's busted. i still have the alty taht overcharged and the mechanic said, chances are the only the voltage regulator is fried and the rest ok.

am hoping to that the vr in my present alternator is ok and swap parts from the other alty as needed.

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  • 4wiseguys Mar 28, 2009

    I have a similar problem, the alternator light on the dash will not come on, yet the charging system seems to work intermittently. Had it in to two separate shops and they could find no problem with the charging system. Went to pick up the car and drive home and the car wouldn't start. Called out the mechanic and found he had left the lights on. We jump started it and measured the output of the alternator. It was not charging anymore. We are going to try a new alternator but the dashboard light issue has me concerned because the Advance Auto website for a replacement alternator says something about a blown fuse in the charge light circuit can cause a "no charge condition". I cant find any such fuse but I suppose a faulty indicator light would be the same as a blown fuse (?). Any comments or advice appreciated!

  • romaq7705 Apr 05, 2009

    sorry for the delayed response.

    fixed the problem and it's the voltage regulator. the guy at the shop couldn't explain why the battery isn't charging but the idiot light is off. the job of the idiot is to tell me that somehting's wrong with my charging system- undercharging or overchargin, the light should come on.

    anyway, changed alternator and charging problem gone. am getting 14.2v no load and 14v with everything on, ac, stereo, headlights (hi beam).


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  • 14,036 Answers

Sound voltage regulator. you need 13.5 14.5 to charge battery .12.volts not enough. dash light warning light bulb could be burn out.

Posted on Apr 05, 2009

  • Jonah Oneal Apr 06, 2009

    do you have the dash manual.that come with car or haynes manual . there is a alternator fuse in your fuse panel.its usually a 10 amp fuse.look in fuse panel in engine compartment or dash .also look at your alternator fuse link wire.


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