Thanks man, lots of good tips there. I checked the alternator and there was no current coming from it so I had them check it at Auto Zone and sure enough, it was defective. Now this kind of worries me, I'm hoping something isn't causing the alternator to go bad. Last night when I checked, I was getting a negative voltage off the battery while the car was running, which was still lower than while the car was off. Either way, I'm gonna check all that you have said here and I did pick up some 4 gauge wire to run since my next project will be finishing my system. They were out of stock for the new alternators so I have to wait til morning to get another one, and when I do I'll update you guys. This is just ridiculous though, but thanks a lot for the help everyone.

if you have the option, dont by the cheap parts. this is usualy what happens.

i could never agree more....

Test how many amps your alt is putting out (put wire coming off) with an amp clamp while it's running.

I don't remember off hand what's high.. but normal I'd assume to be about 20, maybe 30... more if the headlights, subs, blower, etc are on.

New alternator, light still on..

have you check for battery voltage at the altinator?

It seems to me there's no current coming from the alternator. After reviewing the wiring diagrams, all I can really think of is the in-line fuse between the alternator and the started is blown or something in the PCM is messed up, causing the alternator not to produce a current. I'm going to go check that in-line fuse and do some more tests but if that fuse is good, I'm gonna have to have someone with more knowledge take a look. From what I understand, there is a voltage regulator in the alt itself, and that would determine the current coming out of the alt. If everything is fine and the alt still isnt putting out current, the PCM isn't telling the voltage reg. to produce a current, thus the reason no current is coming out of the alt.

Ah, if the regulator is all one piece with the alternator then the PCM is doubtfully an issue, since the regulator is a sefl contained unit.

You got a pic of the wiring diagram? For some reason the site I use at home here froze whenever I tried it.

But yes, sounds like the circuit feeding voltage to the alt is the issue. Check the fuse, check all the connectors it goes through, etc to find where you have an open or whatever.

I checked the voltage at the alt with the care turned of and was getting ~12 volts, so I know its not the fused wire by the starter. I'm gonna go see what I can figure out with the sensor wires going into the alt and ill snap a pic of the wiring diagram.

Okay here's something interesting I just figured out. When testing the positive wire going into the alternator from the starter, with the neg. probe on the battery post I get nothing. When I disconnect the negative post from the battery and check the same wire with the neg. probe on the battery itself I get ~13 volts. I then hooked the battery back up, one probe on various parts of the engine, pos probe on battery and im getting around 13 volts again. It seems there is something with my negative battery cable that has something to do with it. I dont understand why it will make a full circuit on the battery itself, but when the batter is hooked up and i check on the post, theres nothing. I have nothing shorting out and the battery doesnt drain unless the car is on. What am I missing here?

I took a pic of the wiring diagram and will post in a few minutes when I find the cord.

Bad ground on batt maybe?

whoah whoah whoah, ok, there's something very important you have to know about measuring voltage.

*When there is a break in the circuit (ie ground removed), you will always find voltage across that break!*

When you take the ground off, and put one lead on that neg post, you're measuring across the break, thus system voltage. If you were to put your voltmeter leads on the negative cable and one on the negative post, you will read system voltage.

That's very important to know. So is this:

The voltmeter measures drops in voltage.. or difference. When a circuit is closed and working properly, loads (resistance) with current through them "use" voltage so to speak. If you have two identical light bulbs in series, one will "use" 6V, and the other will "use" the other 6, leaving almost nothing at ground (it'll be a very minute reading, in reality). Measure across one bulb and you'll see 6 volts, because the 2 voltages will be 12 on one side, 6 on the other. Hope that makes sense.

NOW, remove ground after the 2nd bulb. No more current can flow, THUS, there's no voltage drop across the bulbs. If you measure across the break in ground you will still see 12V, because the voltage "pressure" is still there, and no current = no voltage drop across loads.

Ok i'm gonna double post here.. stay tuned.

Now, that red wire coming into the alternator from the battery/starter.. that looks like it's constant hot/ charging lead (aka the big wire bolted to the back).

That should, when you touch from the bolt on the alt to any metal with the two probes, be 12v. No matter what.

Orange must be a little wire on the harness it looks like. Should see 12v at run/start.

The other two wires look like "status" signal wires going to the computers.. I haven't dealt with those, and I'd only be guessing anywhere past there in the circuit. However.. if the regulator is all one unit with the alt, that should be irrelevant to the charging output. (that's my theory.. I guess) .

kfjsdlkjf I'm feelin a little shaky on just what it could be, ugg. Rig up a little test light, and go from ground to the bolt on the back of the alt.. does it light up with the car running? Does it still light up with the car off?

If it lights up with the car on, but then goes out when it's off, it's the fusible link on the big wire.

If it stays on when the car's off, the big red wire side of the circuit is ok...

hmmm, I really wanna get my hands on this car, it's easier than trying to explain lol.

the pcm comands the altinator to produce voltage. it can also very the ammount of amps/volts produced. such as under WOT it will command NO voltage leeving less strain on your engien. just like the a/c compressor wont work under WOT. that has nothing to do with your problem but just saying your pcm does have that kind of control. ill search GMSI and see if i can find anything sufull. i know theres a way to test the command circuit from the PCM. i velive i got my shit inline...

"My" shits at the bottom.... have fun :p
GMSI:


Generator
The generator features the following major components:

• The delta stator

• The rectifier bridge

• The rotor with slip rings and brushes

• A conventional pulley

• The regulator

The pulley and the fan cool the slip ring and the frame.

The generator features permanently lubricated bearings. Service should only include tightening of mount components. Otherwise, replace the generator as a complete unit.

Regulator
The voltage regulator controls the rotor field current in order to limit the system voltage. When the field current is on, the regulator switches the current on and off at a rate of 400 cycles per second in order to perform the following functions:

• Radio noise control

• Obtain the correct average current needed for proper system voltage control

At high speeds, the on-time may be 10 percent with the off-time at 90 percent. At low speeds, the on-time may be 90 percent and the off-time 10 percent.

Circuit Description
The generator provides voltage to operate the vehicle's electrical system and to charge its battery. A magnetic field is created when current flows through the rotor. This field rotates as the rotor is driven by the engine, creating an AC voltage in the stator windings. The AC voltage is converted to DC by the rectifier bridge and is supplied to the electrical system at the battery terminal.

When the engine is running, the generator turn-on signal is sent to the generator from the PCM, turning on the regulator. The generator's voltage regulator controls current to the rotor, thereby controlling the output voltage. The rotor current is proportional to the electrical pulse width supplied by the regulator. When the engine is started, the regulator senses generator rotation by detecting AC voltage at the stator through an internal wire. Once the engine is running, the regulator varies the field current by controlling the pulse width. This regulates the generator output voltage for proper battery charging and electrical system operation. The generator F terminal is connected internally to the voltage regulator and externally to the PCM. When the voltage regulator detects a charging system problem, it grounds this circuit to signal the PCM that a problem exists. The PCM monitors the generator field duty cycle signal circuit. The system voltage sense circuit receives B+ voltage that is Hot At All Times through the GEN BAT fuse in the underhood junction block. This voltage is used by the regulator as the reference for system voltage control.

Charging System Indicator
The IPC illuminates the charging system indicator when the following occurs:

• The PCM detects that the generator output is less than 11 volts or greater than 16 volts. The IPC receives a class 2 message from the PCM requesting illumination. The IPC sends a class 2 message to the body control module (BCM) indicating that the charging system indicator is illuminated. The BCM sends a class 2 message to the radio in order to activate an audible warning.

• The IPC performs the displays test at the start of each ignition cycle. The indicator illuminates for approximately 3 seconds.

• The ignition is on, with the engine off.

• The ignition is in the accessory position.









i encluded that scematic so that everything i posted fits together. all the dagnostics i see on SI include the use of a techII or a scann tool with the ability to control the vehicle, and a battery tester. obviously your batterys good and your genrator SHOULD be good. my best bet to you would be to start by voltage-drop-checking the gray wire and the small red one. (im asuming you have a L61??? im not caught up on my RPOs. and all this is from an '04. i would emagine it would be the same).
i would also start first cuz its easy and simple... unplug your PCM and your Alt. check for a short to ground on the little wires (gray and the red one) if you have a short to ground on either then the voltage on those wires are going to be pulled down and the pcm/alt. will never see it and probably not turn it on. while your at it and have the citcuit ISOLATED check ohms of the wires. its not the best test but it wil tell you if you have a broken wire.
if anyone sees fault in what i wrote plz let me know. im learning here..

You are correct, that was a very dumb assumption considering I have taken a class on electrical engineering. It was a long day I guess haha. But alright, I checked the harness wires, the red "control" wire has 3.98 volts flowing through it with the engine running. Im gonna change out this fusible link now and see if that changes anything.

Good diagram up there for sure!

Red wire having 4v should be enough... all that does in all the other cases I've seen is "tickle" the solid state regulator, telling it to turn on and let the field winding current flow.

Also, by voltage flow, do you mean there's an actual DROP in voltage on the wire, or did you backprobe on the alt and measure between the red wire and ground?

I assume you mean the second one, where 4V is present at the connector when measured to ground.. in that case it would be good.

If you've got something at red and 12v at red there is no reason the alt shouldn't have 12 (or 14v, w/e if you wanna be techincal) measured at the bolt when it's running, even if the fusible link is shot I'm pretty sure..

something's not adding up.

If it starts, it should be, but is is your engine ground OK?? measure between a bolt on the engine (any one) and the negative battery post... you should see like .02V or something tiny like that.

Hopefully it's just the link though.. ug toughy...

I may be wrong about the turn on wire... it might need 12V, I dunno... I'm gonna ask around the shop tomorrow, maybe someone knows just what voltage is supposed to be.

im pretty sure its only supposed to be 5v. its controlled by the computer and usualy those circuits usualy are 5v only.

Well it sounds like there a fault in the regulator and or the PCM has a ground wire touching it to cause the battery light coming on...

just for kick did you have the Alternator bench tested?