Weird Alternator Problem

'95 Grand AM 4 cylinder. The dash has both a volt meter and a battery indicator light.
When driving on the freeway (about 3000 RPM) with lights on, fan on high and
the rear window defroster on the volt meter reads about 13.7 which is normal. The problem is whenever I use the turn signal or power windows, the battery indicator light will flicker. The volt meter does not drop below 13.5 volts. I would expect that an amperage issue the voltage would drop quite a bit.
The weird part is when the engine is at idle I can stall the power window and the voltage will drop to 10 volts but the battery light will not turn on.
The alternator is fairly new and was on the car when I bought it
Any ideas what this means? Is the alternator going bad?
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Scott Buchanan wrote:

I don't know what you mean by "stall the power window". Anyway, it seems like everything works fine until you use the power window. This seems like the problem is in the power window. Is it just one of the power windows or do they all make this problem appear?

Hank
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The alternator is fine. It ain't broke so don't fix it.
Stall the window?? Explain that.
Dave S(Texas)
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When the window is either all the way down or all the way up, and the button is depressed, there is still power going to the motor but it is not turning and the motor is stalled drawing the most power that it can.

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Ok....the window buttons are the control method used for the grounds on the reversible motors. There is no power at the buttons, only ground. The motors have a constant power supply. So as others have advised, you have some grounding problems. I'd begin with the battery cables/connections. New cables can fix a lot of weird electrical problems and if those cables are the '95 originals they would be my #1 suspect.
Dave S(Texas)
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When I see swingy alternator gauges on a GM, the first thing I check is the wire mesh strap that usually runs from a bell housing bolt to the body. When this totally fails, it starts to melt the small black wire that runs from the battery to the fender.
Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Jan/06 http://www.imagestation.com/album/pictures.html?id !15147590 (More Off Road album links at bottom of the view page)
Scott Buchanan wrote:

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I agree with Mike. Look for a grounding problem, OR a main power feed problem. The connectors through the firewall where power comes from the under-hood area into the passneger cabin are often the "choke point" and any corrosion there can cause behavior like this.
To verify, measure the voltage AT THE BATTERY TERMINALS while idling with the turn signal or with the power window straining. I'll bet you don't see nearly as much voltage drop at the battery as you are seeing on the downstream side of the firewall connections and chassis ground straps.
Mike Romain wrote:

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First thing I would do would be to check the belt tension....
I used to do a graphic demonstration to my students of simply loosening the alternator belt slightly on a running engine - not enough to make it squeal, but enough to affect output.
I believe a large percentage of alternators are sold by simply hooking up a voltmeter and observing a lower-than-normal output - without paying attention to belt tightness.....I have "fixed" many alternator problems by simply tightening the belt.
When the new alternator is installed and the belt tightened - of course, it reads within specified voltages.
There MAY be more slippage at higher speeds than at idel - which MAY explain the strange behavior.
It has also been shown that a loose belt is much harder on the alternator bearings than one that is tight.
Loose belts generate a lot of heat by slipping on the pulley - overheating the bearing and causing the lubrication to disappear.
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This car has a spring loaded idler/tensioner so there is no way to adjust it. How can I check for proper tension?

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I check my belts by taking a cold off engine and seeing if I can hand slip the alternator pulley. If I can make it slip by hand it will slip under load and could make the volt gauge really swingy. That is what it does on my Delco alternators.
If you can't hand slip it, it's not an issue. That dead ground strap is common.
Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Jan/06 http://www.imagestation.com/album/pictures.html?id !15147590 (More Off Road album links at bottom of the view page)
Scott Buchanan wrote:

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Okay, so you are measuring the voltage _at the battery_ and it's good.
But, the voltage somewhere else in the chain where the light is triggered (where is that???) drops when you use the windows. Therefore there is a high resistance between the battery and that place in the chain.

The voltage WHERE? The voltage measured at the battery, or the voltage on the panel meter? If it's the voltage on the panel meter, find out where the panel meter is measuring the voltage, and find out what is between that and the battery.

Probably not, since the battery should be carrying whatever load there is. Knowing that car, I'm going to suspect a bad ground connection somewhere in the panel circuit, but it could be a bad power connection somewhere between the battery itself and the point where the voltage is sensed for the panel metering. --scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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