My daughter and son-in-law have discovered that the battery indicator (Red) in the instrument cluster is on. I checked the voltage with DOM meter with the car running: 13.68 Volts and without the car running : 13.3 Volts. I wonder if the alternator has a blown diode? Does anybody know what is setting this and keeping it lite. The car is cranking fine for now.

What should I be reading for a good Alternator / battery voltage?

I don't have a scope or a scan tool yet.

Any sugestions?

Thanks.

DRB

Hard to diagnose without more info, but some general suggestions.

first, check all the fuses.  charging lights usually work opposite of most things, they go off because there is power on both sides of the bulb (no potential difference) and if a fuse is blown one side will not have power.

there is an alt fuse in the underhood fuse box, and a gauge cluster fuse in the dash fuse box.

The alternator should have three wires attached, there is a large one with a nut on the back, it should be exactly the same voltage as battery.  The small plug in connector should have two wires.  there is an orange one, it gets power through the alt fuse, and should be battery voltage also.  Unfortunately the third wire, a small red, is pcm control, and without a scan tool or scope i know of no accurate way to check it.

Your voltage reading sounds low, but conditions affect it's reading.  If the vehicle is idling and there is load on the electrical system 13.7 volts is possible.  racing the engine up to 2500 rpms should cause the voltage to rise.  in general voltage is more likely to be about 14 volts.

But the big problem is amperage, not voltage.  without any kind of amp reading further diagnosis is difficult.  that vehicle shows 2 possible alternators, 105 and 125 amps.  

there are 9 diodes in the alternator, any one failed could cause the light to come on. So could a fault in the internal voltage regulator.  There are actually three seperate alternators wrapped up inside the alternator housing, it sounds like one of them has failed, you are getting 2/3 of your rated output, so the battery stays relatively charged, but the light comes on.

For the technical purists out there, I have simplified a bit, the gentleman did not ask for a reference book, just a simple answer!

If you are a gambling man, odds are probably 99% that it is simpler to go and get a rebuilt alternator!

Morning Danny,
The PCm sends a 10 volt signal to the alt sense wire(small red) Try turning the key off, disconnect this connector and use your DMM to see if you are getting the 10volt signal from the PCM when you start the engine, This should rule out the PCM as the reg can short out the  stator wire.The reg works independently of the PCM. You could also monitor that wire with the connector connected and see if it turns off-on(10 volt) A Scanner may show more of how this works, I use a Tech 2
Regards,
Dave

I got your private E-mail. Sorry that I don't respond to any links, if you wish for me to send you an e-mail, you have to allow it on that end.