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Alternator wire question 200

posted by  mshelby on  Wed Sep 22 02:22 CST 2004
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I am trying to track down a short in my charging system that is not allowing the alt. to keep the battery fully charged. I have a new battery, Alternator and Voltage regulator and have had them tested -checked out fine.

I have the infamous "idiot light glow' problem and have decided it is most likely a short in a wire somewhere.

I have two possibilities:

1) radio installed is a recent aftermarket brand which the previous owner installed or had installed. I thought they had 'wired' it up so that you could turn it on even if the key was not in the ignition. Thinking that might be the culprit I pulled it out and it appears to be a standard install with only the power plug and speakers plug and antennae going into the back of the stereo -so I think this is ok. I was wondering if any other owners stereos are powered even with the ignition off.

2)The smaller red wire on the back of the alternator (not the ground or positive wire) doesnt seem to be cycling any current through it. (I used a testor) Is that smaller wire just for the in dash idiot light? If so it is comming on just fine... or could this be my problem?








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    Alternator wire question 200

    posted by  justin21x on  Thu Sep 23 03:36 CST 2004
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    last visit: Tue May 13 08:24 CST 2008
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    I just had to replace the whole wiring harness for the engine. The alternator was definately one of my bigger issues. The small red wire had a short, and the alternator wouldn't charge unless I got the RPM's over 3,000. Replaced the wire, ran it around the inside of the fender instead of up and through the engine. Now the wire is no where near the engine and all works great. My car is an 86 and so has the fabled bad wiring harness where everything rots and shorts out. I eventually had to replace the wire from the alternator all the way back to the harness that's mounted on the firewall, just above the heater hoses that go through the firewall. A continuity test on that wire wouldn't have worked for my case because all four wires coming out of the harness were all shorted together. The radio, I think, shouldn't be a problem at all.

    --
    '86 245, 180K








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    Alternator wire question 200

    posted by  someone claiming to be 240snowmobile on  Wed Sep 22 05:26 CST 2004 [RELATED]

    "I am trying to track down a short in my charging system that is not allowing the alt. to keep the battery fully charged." This is a bit ambiguous. Is it actually a "short" in the charging system? Is there a phantom load that kills the battery when it sits? What exactly are the symptoms?

    1) If your radio is digitally tuned and/or has a clock, it will have a +VBat wire for constant power to retain the station presets and the time. The drain, however, is vary small (milliamps) and would take many weeks or months to kill a healthy battery.

    2) The alternator field winding gets its initial power from the battery through the dash lamp. When the alternator is spinning and generates its own juice, it doesn't need the power through the lamp and the lamp will turn off.








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    Alternator wire question 200

    posted by  someone claiming to be 81242DLB21FCA on  Wed Sep 22 04:53 CST 2004 [RELATED]

    Does the glow go away if the small red wire is unplugged from the alternator? If so, it means that for short intervals the alternator output is dropping below battery voltage. The incandescent bulb averages these to a dim glow like a low continuous current. Is this and internal or external regulator? The radio power has to go to a fuse or power source that is hot when the key is off. If the radio has its' own inline fuse then it can get power from the high side of the fuses that go directly to the junction box on the left fender and not through the key switch. If no fuse then it should go to the low side of a similar fuse.







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