Alternator not charging battery

Old 06-18-2019, 06:45 PM
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Question Alternator not charging battery

The battery light came on, indicating either a bad battery or alternator. The battery checked out OK, but with or without the engine running, the voltage at both the battery and the alternator were 12.2 V (the battery voltage after charging). So I replaced the alternator. The battery light went out, but the battery voltage is slowly going down, indicating the alternator still isn't working. So I checked the voltage to the regulator. I unplugged that connector to the alternator, which only has one red wire going into it (is that right?). Checking the voltage at the connector (with the key turned to the on position), I got nothing. So I'm assuming that is the problem. i'm having a hard time tracing the wire back. The questions I have are:
1) Where is the other end of that wire?
2) Is there a fuse in the circuit? It doesn't look like there is a fuse for this circuit, but I checked all the fuses under the hood anyway (they're all OK).
3) Can I just run a new wire from battery + to the regulator connector?
Old 06-19-2019, 08:49 PM
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Many vehicle charging systems have an inline fusible link between the alternator and the battery which will literally burn up if too much current is being fed to the battery. It is located inline between the output of the alternator and the positive terminal of the battery. If you do a resistance check between those two points with the car off, I suspect you will get an open circuit. This would be why your alternator is not charging the battery. The fusible links are replaceable but the real question is why did the first fusible link blow in the first place? Probably a large current Spike from the former alternator when the internal voltage regulator went South.

The voltage at the output of the alternator referenced to alternator case ground should be about 14.4 volts with no load attached meaning no battery. Actually with the battery attached and current actually flowing, 14.4 volt is a reasonable reading because a healthy battery does not have very much internal resistance. Otherwise it would suck as a battery.

Just look between your alternator and positive battery terminal to find a thick wire that connects the two and you should find your fusible link
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