Man, you've got some weird crap going on. Your engine doesn't have any kind of under-drive pulleys does it?
The biggest thing that would be sucking power with no other accessories on would be the ignition.
What kind of a setup are you running?

 

Everything is stock on this car, no underdrive pulleys and the ignition is all stock. I have checked so many possibilities and replaced so many of the "obvious" culprits that I really have no idea where to go next. I know the headlights cause the major draw but if the alternator is not charging to begin with, I would think any accessory would cause a draw/drain if it's turned on and not charging wouldn't it? I haven't changed anything electrical or messed with the wiring in this car since I bought it last summer, excluding trying to isolate the cause of this problem.

 

Did we have you check your battery cables, primarily the ground, as well as your frame to engine ground? Also, do you have a separate ground wire connected to the alternator? How do you have all your grounds connected? As a test, take a jumper cable and clamp it to the body of the alternator, and the other end directly to the negative terminal of the battery. A bad ground from the alternator to the battery is going to build up resistance, and lower voltage output. It's gotta be something with your wiring, as the alternator tests fine out of the car. See what happens. If the jumper boosts alternator output, you have a ground issue.

 

I'll try that with the jumper cable tomorrow. The battery cables are both pretty new and in really good shape. Everything is tightened up good. The ground from the engine is bolted to the firewall. No separate ground from the alternator, just the negative battery cable on top of the alternator bracket. There is a ground strap from the negative battery cable to the inner fender. There is also a ground (looks like another battery cable) connected from one of the starter bolts to the frame. All grounds are connected with a bolt and star washer.

A little bit more weirdness this evening after I put the alternator back in the car. I jumped it and immediately threw the tester back on. It showed 12.8 volts this time and stayed right there. I turned the headlights on and it dropped to 12.1 and actually stayed there. Almost got excited for a second... That's actually progress in my eyes! LOL The alternator itself started making a squeaking sound, not the belt and then went away. I drove the car about a quarter of a mile and came back, on the way back the alternator started making more noise and everytime I hit the gas, the voltage would drop, lights would flicker, tach would jump all over. I parked and left it running (barely) and I double checked to make sure the belt was tight and confirm the noise I was hearing was the alternator itself and not the belt. The alternator was hot as hell!

The thing that gets me most is that there never seems to be a constant with this issue other than not charging/starting.

 

From the negative battery cable to the alternator makes for a good ground. A jumper cable won't be any better than that as far as the alternator is concerned. I only see one possible weak link with your ground circuit. The only ground to the frame is jumped from the starter. So your engine is the conductor for ground that's at the alternator, which is fine as long as there isn't any rust or paint insulating those connections. I'd be curious to take the ground jumper cable and connect it to different places like the frame, engine, and firewall to see if anything happens. Also, if you were to take that ground cable off the alternator, and put it on the same bolt for the frame ground at the starter, I feel that may be a better connection. For engine ground, I actually prefer one of the motor mount bracket bolts to the block. Let's see what your test turns up.

 

I don't think the ground from the alternator will reach the ground on the frame from the starter. I'm going to reground the engine ground that's on the firewall currently, you're saying a motor mount would be a better choice for that one? Not sure if it's Ziebart or some kind of undercoating but the firewall has been sprayed with something and that ground just doesn't look like it's very good. I'll try the ground jumper cable tests at various places and see what happens (as soon as it stops raining) and let you know. I was reading last night about possible causes of low charging system output and ground issues were always noted, either too many or not enough. Also, 10 gauge wire should be sufficient from the alternator to the battery correct? I have some 4 gauge lying around but didn't want overkill. The way the Camaro behaved last night was bizarre even for current standards. There's not really much adjusting I could do on this alternator but the noise it was making when I started it yesterday has me a little scared. I know it wasn't the belt I was hearing.

 

Not necessarily to the motor mount is a better place, I just like it better because it's there to stay. As opposed to on the starter where it could get in the way. Personal preference. On mine, I have the ground cable from the battery to the engine, then smaller wires or straps distributes off the block to frame and firewall. If you have undercoating goop on the firewall, just scrape it off where the connection is. Again, how I run mine is all personal preference.

 

Should I definitely have a ground from the engine to the firewall? The rain is almost done and I'm heading out to check connections/grounds etc. just wondered if that ground on the firewall would be ok if I moved it to the frame or somewhere else? If it should be on the firewall I'll scrape the crud off and retighten it.

Also, been meaning to ask about the old wires from the 3 wire. I'd like to get them outta there but don't want to cut them. The main power wire from the back of the old alternator goes to the starter and I unhooked that one. Where do the other 2 wires go?

 

You definitely want a ground to the firewall, to ground the body well. A number of things inside your car need body ground. Connecting only to the frame may ground the body in a roundabout way (through the subframe mounting bolts), but it wouldn't be a great ground. For the other two wires at the alternator, one goes to the idiot light, and the other is the exciter wire (activated the voltage regulator) that splices into an existing hot lead in your harness.

 

I checked all the grounds again and redid the ground on the firewall. Decided to replace the 10 gauge wire from the alternator to the battery with 8 gauge to see if that would do anything. Started the car and let it run for a minute or two and put the test meter on the alternator and got 14.1 volts! Then I turned the headlights on.... Meter dropped to 11.3 and slowly started dropping more. I turned them off and went back to 12.33 and stayed there. I tried the ground tests on the engine, firewall, fender, frame, alternator, my dogs choker chain etc. and it stayed at 12.33. I drove the car for a mile without the headlights on and the gauge stayed just under 13. Just before I got home I turned the headlights on and the gauge dropped down around 10-11 and kept going lower. Car would not restart of course. This really sucks, I could've individually hand wired this car all over again with the amount of time I've got into this problem going back to last summer. Sorry to complain, I've had it with this. Got far more enjoyable work to do on this car is all.