Battery light on instrument panel


Old 11-24-03, 06:20 AM
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Battery light on instrument panel

I have a 1987 S-10 truck. 2.8L engine. Automatic/Air.
Recently, my battery light has been coming on. Sometimes it stays on for quite awhile, other times it on and off, and sometimes it just flickers on and off.
I had alternator and battery tested and were ok. I have been told it may be a loose wire, an almost broken in to wire.

The only thing I've noticed is when driving at night. The instant the battery light comes on, my headlights become brighter. They don't flicker on and off. When the battery light goes off, they just return to normal.
It seems to me that the voltage regulator has failed, and is allowing alternator to overcharge.

Any suggestions?

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Old 11-24-03, 09:51 AM
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Join Date: Jan 2001
Location: Kansas City, Missouri.
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Hi knucklebuster,

You have a puzzling post. Often a alternator test and battery test will point to either the battery or the charging system. Your test did not reveal this. I do not know if you performed a handheld test or a bench test, each with their own pro's and con's.

The remark '..headlights become brighter...' raises many unexplained questions. Since your battery light only occurs intermitently, one simple and sure way to pinpoint either the battery (connectors, cables, etc) or the charging system (alternator, wire harness, regulator, belts) would be to get a voltage reading at the time that the dash battery light comes on.

Use you own creative ideas. For example connect a cheap VOM to the leads off on old cigar lighter adapter and plug it in and go for a drive. Then report back the readings. You should expect to find voltage readings in 1 of 3 ranges.
- under 13.5 volts
- between 13.5 and 16.0 volts
- over 16.0 volts

Depending on your reading, we can point where to look next.
Old 11-24-03, 10:09 AM
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I was in a bit of a hurry when I posted the original post. What I don't understand is if it was a short, I would thing the headlights would dim instead of brightening.
If I have a loose connection somewhere, I would think my lights would go on and off.
The way it is, it is like using the dimmer switch.

I had battery and alternator checked at an auto parts store with a machine they rolled out to the vehicle. And the battery light was going on and off while they were doing the test.

When the test was finished. It indicated a good alternator and battery.
Old 11-24-03, 02:28 PM
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Join Date: Oct 2003
Location: Boynton Beach Florida
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Those tests aren't thorough enough to find the type of problem your having. It does sound like the voltage is intermittantly spiking too high. The most likely cause is the voltage regulator which is built into the alternator. The only way your going to verify this is to have a volt meter connected all the time so you can see what it does when the light comes on. I've never seen one come on for high voltage before though. If that's really happening, you need to get it fixed quick before it starts taking out everything electronic in the car. Especially the ECM.
Old 11-24-03, 04:56 PM
Join Date: Apr 2002
Location: Pittsburgh,Pa
Posts: 2,417
Awhile back(about 1978)a guy said he needed new headlights that they were all burnt out.Being the curious type I checked the voltage at idle on that old Dodge 23 volts, bet those lights were bright also,at least a little while.4 new headlights and a voltage regulator and away he went.Yes you need to see the volts when the problem occurs.Likely you will need an alternator though.
Old 11-24-03, 05:43 PM
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A big thanks to all that replied to my post. I am going to remove alternator and take it back to where I purchased it and let them bench test it.

I talked to one of the sales associates today and he said that if bench test does not show any problems, he would go ahead and exchange the alternator if I insisted.

Sooo, sounds good to me.

BTW...great forum!
Old 11-24-03, 06:25 PM
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Join Date: Jan 2001
Location: Kansas City, Missouri.
Posts: 1,172
Since your problem is intermitent, and has symptoms of voltage spikes, I would definately take advantage of the offer to replace it as offered. If they change there tune when you get there, then remind them of their agreement and remind them that the problem is intermitent. Good luck.

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