My voltage guage reads 15-16v all the time when the engine is running. I replaced the alternator (the old one was at least 15 years old), and it made no change at all. I'm afraid this is going to eventually fry my battery or my ignition electronics.

what are some possible causes?

thanks,
Brian

Try another gauge. Like a real volt meter to verify that the voltage is that high.

After checking the real voltage... internal or external regulator? Controlling system voltage is the job of the regulator and if you do not have an internal regulator replacing the alternator would do nothing.

After checking the real voltage... internal or external regulator? Controlling system voltage is the job of the regulator and if you do not have an internal regulator replacing the alternator would do nothing.

To be honest, I don't know, how can I tell?

Snap a photo if youre not sure and we can identify it for you. If its stock its externally regulated. The regulator is ussually on the drivers side behind the headlight. I would suggest hooking a volt meter up to it to get an accurate test. A weak gauge would give you this problem, But more then likely your problem is a sticking regulator. If the gauge is weak then with the key on engine off the volt gauge (car volt gauge) will read higher then 13 volts. If its like that probably gauge problem if its around 12.6 volts then more then likely a charging issue. Paul.

The original externally regulated alternator has a 2 prong plug sticking out of the rear of the alternator, while the later internally regulated type has a plug sticking out of the side of the alternator. If you have a service manual, you could look in there for a picture that would be better than my explanation. Or take a look in the Tech Reference section of this site, which has a good article on alternator upgrades.

I must have the externally regulated setup then, I only have the 2 prong plug on the back of the alternator, and my 'hot' wire has a lead attached to something behind the battery.
I guess I'll buy a new regulator. I doubt my guage is bad, it is a fairly new Autometer Sport Comp. The regulator on the other hand would have been installed at the factory in 69. Maybe that will solve the problem.

To be honest, I don't know, how can I tell?
Here is a pic of a 1972 externally regulated alternator
http://www.chevelles.com/showroom/data/500/Dsc00886.jpg

The 2 small terminals are like this (l l) it is externally regulated

Heres a pic of a internally regulated alternator

http://www.chevelles.com/showroom/data/500/Alternator1.jpg

If the small terminals are like this (- -) then it is a internally regulated

If externally regulated you will have 4 terminals on the regulator. I believe on a chevrolet they are F 1 2 3. These coorespond to Field, Stator, Battery, Light. You will need to have a volt meter and measure the voltage to each terminal from a common ground. Based on these readings you can determine the source of overcharging. Of course make sure you are using an accurate meter.

Mine's externally regulated, and I had trouble with low voltage and replaced the regulator with one from a local chain parts place, for $14. A week later I had high voltage and whining alternator. The new cheap regulator was bad. Got a new one from napa ($30) and it's been fine since. It is near the driver side headlight, and be sure to make a good ground when you replace it.

I thought I would pass along some info I learned on another forum concerning overcharging external regulators. For those of you who know Ignitionman(Dave Ray), he posted some suggestions on this subject.

Make sure the external regulator is grounded to the engine, through the stock paths, but grounded correctly.

Obtain the Wells VR715 replacement external regulator at Autozone or other parts store, cost about $12 or so. This regulator directly interchanges with the stock Delco and the Delco cap can be used on it.

The stock Delco regulator is a servo type, has solenoids to turn the rotor on and off, and needs adjustment to set the in-out and charge rates. This type turns the rotor on and off as the system needs volts, it also makes for high/low/high/low light operation when the headlights are on.

The Wells is electornic and works like the later internal regulator alternator types. It turns the rotor on and keeps it engaged until the key is turned off, so the charging is always held on with no interruptions. When the voltage rate of 14.6 is reached, excess charge voltage is dumped to ground. This type is more stabile and accurate and makes for less alternator wear.

I thought I would pass along some info I learned on another forum concerning overcharging external regulators. For those of you who know Ignitionman(Dave Ray), he posted some suggestions on this subject.

Make sure the external regulator is grounded to the engine, through the stock paths, but grounded correctly.

Obtain the Wells VR715 replacement external regulator at Autozone or other parts store, cost about $12 or so. This regulator directly interchanges with the stock Delco and the Delco cap can be used on it.

The stock Delco regulator is a servo type, has solenoids to turn the rotor on and off, and needs adjustment to set the in-out and charge rates. This type turns the rotor on and off as the system needs volts, it also makes for high/low/high/low light operation when the headlights are on.

The Wells is electornic and works like the later internal regulator alternator types. It turns the rotor on and keeps it engaged until the key is turned off, so the charging is always held on with no interruptions. When the voltage rate of 14.6 is reached, excess charge voltage is dumped to ground. This type is more stabile and accurate and makes for less alternator wear.

Cool stuff. Just to add, be sure to solidily ground the Wells regulator. Either through one of it's mounting feet or with a ground strap to the case. Be sure to disconnect the battery before installing.

I used to get under the hood and smack the regulator with a screwdriver handle and that usually worked for a while. Although I did like it with the bright dash lights it would blow them after a while.

Make sure your battery is grounded down if not it will read high reading and also your motor to but ground the negative side of you battery to the fender make sure its a solid good connection.

Thanks for the advice so far. I went through and checked voltages as described in another thread I found here, and everything checked out unless I did something wrong. I've tried 2 different regulators, and went over all the grounds under the hood, and still I'm having issues. I've been trying the Sorensen regulators from Advanced.

Now it will sit at 14 volts at idle and low speeds, but if I get the engine over about 2800 rpms for a few minutes then it gradually creeps up to 15-15.5 volts. Stop and it goes back down to 14 at idle. This would seem like a ground issue to me, but I can't find a grounding problem. I'm tempted to return both these Sorensen units (made in China) and order a Delco or try the Wells mentioned above. I wouldn't really be worried about the 15 volts except that I don't want to damage my expensive ignition electronics.

I have another question, what is the little capsule with a single wire coming out that attaches to the side of the regulator? Looks like some kind of capacitor? What does it do?

That is a capacitor and is there for noise filtering. The old external regulators had relay switches in them to turn the alternator field coils on and off. The capacitor kept if from generating radio interference.

I'm tempted to return both these Sorensen units (made in China) and order a Delco or try the Wells mentioned above. I wouldn't really be worried about the 15 volts except that I don't want to damage my expensive ignition electronics.

You may see 15 volts if the battery is really low, if it is fully charged than its a problem. If you are going to be exchanging parts anyway, why not convert to a internally regulated alternator, which is a lot better than the externally regulated ones.

I ended up getting one of the Wells units from Autozone, made in USA, and the problem appears to be solved. it holds rock steady voltage now, below 15 volts.

No more chinese crap for me! I have 2 china made 'sorensen' regulators to return to Advanced now.