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Old 10-03-2009, 11:03   #1 (permalink)
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Intermittent charging system light

Intermittent charging system warning light. Just started - mostly at low RPM. Battery gauge is still centered and volt meter across battery with engine off is about 12.3V. This is a 2002 V6 Explorer XLT with 142,000 miles and the origninal battery. Is this a case of the alternator ready to die? Or what are other possible causes? How do I diagnose it?
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Old 10-03-2009, 12:20   #2 (permalink)
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Re: Intermittent charging system light

It could be a poor connection in the system somewhere. What voltage did you get with the engine running?
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Old 10-04-2009, 14:25   #3 (permalink)
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Re: Intermittent charging system light-more symptoms

With engine running and fan and headlights on, voltage across battery is only 11.2V; with fan and headlights off it is 11.5V. Should be 12.8 to 13.5 V, right?

Now when engaging starter motor the dashboard gauges goes wild - speedometer and tachometer peg out at high end of scale, then drop back when return key returned from “start” position to “on” position.

Loose ground somewhere?
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Old 10-04-2009, 15:15   #4 (permalink)
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Re: Intermittent charging system light

With the engine running you should have around 14.2 with a fairly charged battery. Sounds like you have charging system issues. Check all the connections and you could take the alternator to have it tested at a parts store that does that dor nothing.
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Old 10-06-2009, 05:12   #5 (permalink)
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Re: Intermittent charging system light

Test proved alternator not charging. Trusty mechanic replaced with a rebuilt alternator, replaced 7 year old battery and pulleys. System is charging fine BUT the dash idiot light remains glowing. What is that from and how do we fix it?
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Old 10-06-2009, 08:24   #6 (permalink)
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Re: Intermittent charging system light

Check fuse #15 under the dash and if that's okay, it could be a defective alternator or plug to it. The light green/red wire controls the light.
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Old 10-08-2009, 04:48   #7 (permalink)
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Re: Intermittent charging system light

Thinking the rebuilt alternator may have been defective, my mechanic installed a second rebuilt alternator. But after 2 miles of driving, the charging warning light returned again. Voltage testing and computer scan show it is charging fine. He suggests that there could be a problem behind the dash. He notes that the voltage gauge never moves but it should wiggle when load is applied - like fan on with headlights. It has always remained very steadily centered after ignition start I tell him. Also we checked all fuses. Mechanic says plug and connection are fine. Besides friction tape to cover the idiot light - how can I diagnose / fix this problem? I realize if the alternator conks again I won't get a fair warning under present status of the electronics.
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Old 10-08-2009, 08:09   #8 (permalink)
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Re: Intermittent charging system light

The battery gauge doesn't move very much. You won't see a jump when somethimg is tuned on. That green/red wire is the wire to the light. They should check that wire and it's circuit.
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