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Idiot light off but no charging?
Topic Started: Apr 10 2014, 11:48 PM (637 Views)
Richard123vmt


The light does go on with engine off. I know I am not getting any charging because I tested it with a dvm. I can understand that the alternator may be shot but why would the idiot light stay off? I have also established continuity between the alternator large lug and the pos terminal of the battery as well as tested the fusible link. I have shown that there is no parasitic leak. I did all this by moonlight. Is there another fuse under the dash? In the morning, what other tests can I make to test the alternator? With the engine running I should have 14 volts at that alternator lug, right? What about the other wires to the plug? I don't mind replacing the alternator if necessary but that light off makes me suspicious. I have never seen an alternator stop charging without the light going off. And it is not undercharging--it is not charging at all. Belt is okay. Any ideas?
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Hanuman
"The Almighty Grounds Cleaner"

its happened to me on other cars, alternator fails, no charge light on.
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Old Man


fuse on fender that has a nut on each of the two legs. clean and polish the connections and see if that helps.
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t3ragtop
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Turbo3 and Twincam Tweaker

as well as making sure that the fuse link has not melted. ;)
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Richard123vmt


I found that after charging the voltage at the alternator stud and at the battery positive were identical so I figured that ruled out the wiring. I got an alternator at the junkyard for $30.56 out the door (no core charge), had it tested at Autozone pass, pass, pass, installed it and now I have got 13.30 charging voltage. I will now have the old one tested to see what happens. It is very oily which might be its original problem.
Another day another dollar. I just hate it when the problem lasts overnight.
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Richard123vmt


Thanks for all replies, especially that light on no charge is not unknown.
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Hanuman
"The Almighty Grounds Cleaner"

i havent had a alternator fail on a metro yet, i did loose the belt and that turned on the light.
on both of my subarus my head lights went dim, heater fan slowed down, eventually the radio got dim flickered and shut down....but no charge light.

on my 2003 gmc seirra....i honestly dont remember......
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Johnny Mullet
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Fear the Mullet

I kill alternators all the time with EcoMudder. No light ever.
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Richard123vmt


Old alternator scored Fail, Fail, Fail. Later reading of voltage showed 13.77. Next case!
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Stiffchezze
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Sir Metrologist

Just some FYI,
Our charging idiot light systems read voltage directly off the back of the alternator. It could care less if the battery is getting charged, it just wants to know if the alternator is working.

Ever wonder what those two extra wires coming off the back of it do? :hmm
The white with a red stripe one turns the idiot light on and off.
Also turns the Daytime Running Lights off as well if the alternator stops working.

Your battery could be getting nothing, and as long as the alternator is humming along happily, you get no warning light. The alternator has to be producing (roughly) 0v before it will come on.

To recap, the light ONLY checks the condition of the alternator, NOT if the battery is receiving a charge.
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