Like the title states, I have a new 140amp alternator and a new Optima redtop battery. The wiring from the alt (1 wire) was corroded a bit with the stock connections so when it broke off last year, I replaced it with a wire I had laying around. It was a quick fix to get the car moving. The gauge still read above 13v but after driving it for awhile, especially at night, the gauge would drop below 13v and stall. Barely get it started unless I jumped it. That was last year. Car sat over winter and once the first start up came, it acted fine with a fresh battery. Volts were above 13 and it drove fine, but after awhile it would do the same thing. So I replaced the all the parts mentioned above with new units along with rewiring the quick fix I did last year only to have volts BELOW 13 now. I know for a fact the battery and alternator are perfectly fine. I installed the alt in my buddies '89 TA and his gauge went well above 13. I was searching this but figured I might post this up anyway. I read that it might be a connection problem with the plug? Check the brown wire or something? Is this with the car running or key in the "on" position? Does anyone have a diagram or a pic I can use? Like I said, the stock 1-wire hook up wire was corroded all to hell and I replaced it with a wire that didn't have any resistors or whatever those tube things on the wire were called. Please help me! It's June and I want to drive my car!

13 volts is more than enuff to run.

Your gage might be inaccurate.

Monitor your voltage with a test instrument grade meter because only knowing “it‘s below 13” is not good enuff.

In a properly maintained car you won’t stall above 11 volts.

Make sure all connections are clean and tight from the battery to the starter and solenoid.

What is your idle RPM at when the car is warmed up? If it's too low, the alternator won't turn on. My alternator (Powermaster 140 amp) seems to like 650-700 RPM to maintain full output. If the car idles at 500-600 RPM when warm, the volts will drop to 12'ish.

Turning on my headlights will drop the volts by a full 1 volt. Combine that with low idle RPM and it would drain my battery sitting in traffic at night. With both radiator fans on, the volts drop more as well.

Go to a parts store, Wal-Mart whatever, and buy yourself one of those digital volt guages that plugs into your cigarette lighter. Much better than looking at the dash.

Powermaster has instructions on their website for testing alternators (grounding, positive wire voltage resistence etc). Look up 140 amp models for our cars and there should be a PDF file for it.

Before I rewired the 1-wire hook up going to the alt, it stayed above 13. It would eventually drain but it would be above 13. Now that I have a proper wire in there, it doesn't even come close to 13. I'm going to check the alt plug wiring. Hopefully, it's that. If not, I have a big problem on my hands.

Im going through the same thing...

The car wont run with the neg cable disconnected (Carbureted, mind you) and I'm not getting anything over 12v across the battery terminals with the car running.

The red wire on the plug is showing no resistance to the positive side of the battery, and neither is the red wire coming from the alt case. Both are making good connections. The alternator case is showing no resistance to ground either.

But despite all the connections being good, my battery isn't seeing more than 12v and the car wont run with the neg cable disconnected.

It was doing the same thing with the old alternator, and this is a new one.

I'm at a loss... i see no reason why it shouldnt work.

there has to be a bad connection somewhere, if everything was right it would work.

Do you have a vbelt or serpentine setup? if vbelt maybe check ur alternator belt, make sure its not too loose. that can affect it. And double check the wiring you fixed that the connection is nice and tight and nothings corroded.

I just realized something...

I've got a vid of me driving the car the other day and the voltage was fine, and the battery was charging fine.

I had just gotten the car abck on the road, and decided to do somethign about my fan wiring (I was tired of poppnig the hood every time and wiring it to the battery terminals). My first attempt was to run it off the fuse box from an ignition power source... well apparently that's a horrible idea and I have it wired up properly through a relay right now. You live and you learn. But when I had it running through the fuse box, I saw some blue sparks out of the fuse box and now neither of my IGN slots are working anymore. I think that's when this started.

Any idea how that could affect the alternator or its ability to charge the battery?

I see two big fat red wires coming from those ignition slots that dont work... Where do those lead?

Edit: I've checked all the positive wires leading to and from the battery nera the starter and all the fusible links there are fine. Is there some sort of sensor wire that tells teh alternator to turn on? How does that work? Because Im thinking THAT is the problem.

There is a smallish "switched" wire going to the alt plug. It should have 12V on it when the key is on and it should be 0V when the key is off. The other smallish wire going to the alt plug turns the light bulb on. The bulb must be good, or the alt won't charge IIRC. IOW, the bulb circuit has to have a path to ground.

Those big red wires are main power wires to the fuse panel direct I think. But, you must check the FUSE LINKS which I had a problem with on both my firebirds. They are the red wires beside the battery mounted on the plastic peice to the wall. They "CORRODE" and will bring high resistance to the circuit. They also have a built in fuse which may blow. Also our cars have a fuse on a wire right beside the batter on the back of the battery. Check for a blown fuse there. Ground wire problems can also present the same symptoms. Check for Grounds beside the battery and otherwise inside the fuse panel area for broken terminals and bad grounds. An ohm meter or multimeter is very important and useful here. Measure difference in resistance. This will very likely be the cure to these problems.

There is no sensor to turn on your alternator. The wiring diagram can be seen from the Haynes manual. Battery-fuse link-alternator-volts indicator at dash-Fuse panel. Simple system. The problems are usually measured in High resistance with ground or the fuse link wiring. Take that thing off the wall and clean it up. It gained for me about 0.3 volts. I would use a wire brush and battery terminal cleaner. Let me know what you find.