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Alternator light on
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dgordner View Drop Down
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    Posted: Oct/03/2021 at 5:45pm
1970 javelin 304. 30 amp alternator. Tested by an electrical shop. New voltage regulator. I have 10 plus volts in the green wire with key on. Same with engine running. With engine off i have 12.4 volts in the battery. With engine rpm turned up to around 1500 rpm the battery takes a charge up to 12.8 and charges no further. I also have an alternator light on in the dash above idle. When the engine is at idle the light is not on. I am confused. 
Safety is only what one makes of it!!! 1969 chevelle SS 1970 Elcamino SS
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mstrcrftr View Drop Down
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Points: 2066 		Post Options Post Options   Thanks (0) Thanks(0)   Quote mstrcrftr Quote  Post ReplyReply Direct Link To This Post Posted: Oct/03/2021 at 6:52pm
its not charging right based on your voltages.  it should be about 13.4 when running at that rpm. 
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tomj View Drop Down
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Points: 7544 		Post Options Post Options   Thanks (0) Thanks(0)   Quote tomj Quote  Post ReplyReply Direct Link To This Post Posted: Oct/03/2021 at 10:36pm
Sounds like a bad battery, shorted cell or something, assuming there's not other hidden problems. Is it old? Did it sit for a long time uncharged/discharged? They don't like that very much. Take it to a store and have em test it...
1960 Rambler Super two-door wagon, OHV auto
1961 Roadster American, 195.6 OHV, T5
http://www.ramblerLore.com
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dgordner View Drop Down
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Points: 124 		Post Options Post Options   Thanks (0) Thanks(0)   Quote dgordner Quote  Post ReplyReply Direct Link To This Post Posted: Oct/04/2021 at 7:48am
I never heard of a bad battery (especially one with 12 bolts) causing the light to not be on at idle but does come on above idle. 
Safety is only what one makes of it!!! 1969 chevelle SS 1970 Elcamino SS
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bigbad69 View Drop Down
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Points: 6668 		Post Options Post Options   Thanks (0) Thanks(0)   Quote bigbad69 Quote  Post ReplyReply Direct Link To This Post Posted: Oct/04/2021 at 9:36am
The ALT light is on because the alternator output and battery voltage are not the same voltage. Have you measured the two to find out what is happening? Incandescent bulbs are not polarity sensitive.

The alternator could have a bad diode or winding. Do you have a parts store that can test it for you? I would also test the battery as Tom suggested. If nothing else, it will positively eliminate the battery from the equation.

The regulator is new, but is it working? There was a time when new = working, but that time has passed. Just one more thing to consider.

There is another thread here with a similar charging problem that turned out to be a bad sense wire. Check your wiring. It's 50 years old.
69 Javelin SST BBO 390 T10
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tomj View Drop Down
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Points: 7544 		Post Options Post Options   Thanks (0) Thanks(0)   Quote tomj Quote  Post ReplyReply Direct Link To This Post Posted: Oct/04/2021 at 5:05pm
The AMC alternators had various configurations over the years, and there are a lot of subtlely different voltage regulators, different isolation diode setups, as well as bad grounds, bad battery cables, etc. 

Just general stuff: All electrical connections need to be shiny metal. All crimped connections should easily survive hard tugging on the wire. If you wiggle a wire at a crimp, and the cut ends inside move, then it's a bad crimp. 
1960 Rambler Super two-door wagon, OHV auto
1961 Roadster American, 195.6 OHV, T5
http://www.ramblerLore.com
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scott View Drop Down
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Points: 3501 		Post Options Post Options   Thanks (0) Thanks(0)   Quote scott Quote  Post ReplyReply Direct Link To This Post Posted: Oct/05/2021 at 3:39pm
This thread may be of help:  https://theamcforum.com/forum/alternator-charging-system-tests-for-amc-vehicles_topic74295.html 
"Prolly" is not a word.
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