my Z has had an overcharging problem for as long as I have had it. I replaced the voltage regulator and it cut down on the problem, but it still overcharges pretty bad. Could the coil be part of the culprit? My tachometer used to jump on it's own at times before, like it'd go to 3500 rpm's and the car would be totally off. Any ideas?

 

It's likely the alternator isn't original. So check this pick for correct wiring. "E" is a ground. "A" is hot. make sure the condensor is working and hooked up to "A". The wire from your distributor goes to the negative side of the coil.

 

I have three alternators, all original. I switched out the original one before my engine swap with another original one that I bench tested, and it worked fine. My dad suspects that I have a short somewhere. I also don't have any positive wires running from my "A" terminal...what's that for?

 

here's a pic of my question.

 

this overcharging problem just gets annoying...and I notice that my lights brighten and dim the farther it overcharges. I've actually made batteries bubble and almost explode before.

 

That's what I meant by "original". Previous owners. The hot wire goes to your fuse box and then through your amp gauge and back to your starter motor battery terminal. That's how the alternater charges your battery. Does your amp gauge show a charge. The wire in the upper left of the pic is to the condensor, that little round thing. What I think has happened is a previous owner installed a later alternator like from '80s. They have an internal voltage regulator. This is why your system is going crazy, it's fighting itself. I saw a post on how to wire them correctly, I think it was on www.zhome.com

 

my alternator looks identical to the one you showed me, and I also pulled another alternator off of another Z at the junkyard to test, and I was given a third one when I got my other block for free. They are all hitachi alternators, but my alternators have wires that come off of the alternator and connect to the wiring harness, whereas yours the wiring harness plugs into the alternator.

 

oh, and my amp gauge works, that's one of the reasons I know it overcharges. The ground wire was on the other post terminal (not the A), so I moved it to the "E", but it didn't do anything for me.

 

The condensor is important, why exactly I can't explain. All 4 of my Zs have one. I now suspect your regulator or the wires leading to it. It is allowing the alternator to charge to long. The points could be burned and sticking closed. Look inside and if it looks okay we may have exhausted our experience and it's time to take it to an auto parts store that will test the charging system for free. Some of the better ones do this.

 

hahaha, the regulator is brand new. The old one had good clearances on it, but I replaced it nonetheless a while ago. I don't have one of those condensers...do you know where I could get one?

Since I put that voltage regulator on, it made the car overcharge a hell of a lot less, and now it's just a slight annoyance factor.

 

Your alternatot won't work unless it's hooked up right. I clarified the pic here. You can get a condensor at the auto parts store.

 

yeah, the alternator is hooked up correctly, just as your diagram is, I just don't have that condensor. Hopefully that's the problem, because it'd be an easier fix than finding all of the body grounds and cleaning them.

 

The condenser, physically, is the same as one on a distributor in a points ignition system: they're just capacitors. Functionally, the one on the alternator helps eliminate the annoying buzz in radio reception that you'd otherwise have, and it helps somewhat in regulations, so it sure couldn't hurt to add it in your case (and it should be cheap, too). You can kind of think of them as electrical "dampers". While that's not entirely accurate, it's close enough and sort of gives an idea of what they're supposed to do. Another explanation I saw, that made some good sense was: "Capacitors are basically waiting rooms for electrons". I love the S30 Z's more than any other car, but the 20 plus year old electrical system can sometimes try your patience. Is your fuse box in good shape? The 240 is kind of notorious for current-sucking shorts on that because it's a high-tension fuse box. Sport Z had a nice article about it a few issues ago. Good luck!
Dave

 

More on condensers- The early Z alternators are 3 phase AC. The purpose of the condenser is to convert the AC to ground which is why it is hooked up to the hot side and grounds itself. The one on the distributor discharges the high voltage from the coil to keep the points from arcing and burning which is why I thought maybe you regulator was staying on to cause the overcharging. Stay in touch on this one.