Have a 68 400 covt and I am reading about 17-18 volts (with hand held meter) when the car is running. I assumed it would be a bad battery, voltage regulator, or alternator causing the problem. I just replaced the battery and still see the problem, about 13-13.5 volts idle and 17-18 running. I notice the regulator is mounted to the front engine bay (driver side) by the radiator. Is this the normal mounting point? Also it's not a GM part (brand name "SELECT") and has a 4 wire plug, the alternator is Delco. Can I just buy a Delco regulator, is the wiring standard? Appreciate any help!!!

I would certainly suspect the voltage regulator. That is a bit high.

With the ignition off, what is the battery voltage?

NAPA has them;
68 FIREBIRD VOLTAGE REGULATOR

The voltage is 12.5V on the battery I just installed today and did not let charge. The reason I changed it out was the old battery was almost dry and had no date on it, I just got the car 2 weeks ago.

High voltage can cook out the electrolyte, or low electrolyte can trigger the regulator to try to charge constantly.

Since you have a new battery, I'd test it briefly to see if the regulator now outputs a more reasonable voltage. If not, change it.

I really appreciate the help,

I'll let it run for a little while and see if the voltage drops. If I do end up replacing the regulator I noticed there are several different models out there and some rated 42A some 63A and some that don't mention the rating. I'll have to check the altenator part number to make sure, but my guess is I need the high amp model since the car has AC. When I look regulators available from Classic Industries there are several options, just like the other link provided by Fbody69 for a NAPA part. Should I error on the heavy side to be safe and should the current harness match up?

The same thing happened to my cammer, after coming back from the Woodward Cruise two years ago. I had a brand new battery get 'cooked' from a bad external regulator.

Buy one from a parts store, not eBay. I learned that lesson the hard way.

Match the regulator to the output of the alternator. 37A alternators use 42A reg, 55 and 63A alternators use 63A reg. A/C cars usually use the 55 or 63A. It's stamped on the alternator case along with the part number. If the alternator has been rebuilt, it may have output higher than the part number would seem to indicate.

'69 changed to internally regulated alternator to avoid the charging issue you are experiencing. The original regulators were electromechanical, with coils and contact points. Most service replacements are transistorized. You can sometimes tell which you have by watching the dome/courtesy/instrument lamps just after starting the car. If you see a flicker, like fluorescent lamps or a computer monitor, you have a solid state regulator. If the lamps merely dim a bit at idle compared to revved up, it's likely electromechanical.

Thanks Yellowbird and everyone that responded.

I checked the alternator earlier and it's 37A, so I will match up the regulator. The car has A/C but is missing the compressor, guess they needed to replace the alternator at some point and elected to go with the 37A. When I finally get to putting a compressor back on I'll have to look at changing out the other componets. For now Im just itching to get it tagged and enjoy before winter. I'll let everyone know how things go...Since this is my first 1st Gen after years of wishing I am sure to have more questions as I correct little details here and there

Most regulators (solid state) don't even bother to state a capacity. The circuitry is likely designed to accomodate a wide variety of alternator outputs. It's only the old coil and contact style (two line AC Delco cover) that are limited in application.

Just check to see what kind of regulator it is, then choose accordingly.

I replaced to voltage regulator today and still have the same problem. I checked grounds to the chassis, engine, alternator, voltage regulator and everything looks good. I checked the wiring to the voltage regulator and verified I have a two good connections from the alternator and a good connection from the battery. All connections appear to be on the correct pins. I also have a single connection from the voltage regulator to a resistor(?) or some single componet that is bolted to the chassis below the regulator. I have a good battery connection to the alternator, but I did note that I have 12.5v on the blk/wht wire with the ignition off and the voltage regulator is still warm to the touch after the car has been sitting idle.

My symptoms still are 12.5 volts idle measured at the battery and on the voltage gauge connected to the fuse panel. Once the car is started the voltage jumps to 17-17.5v and will increase to 18v when I hit the accelerator.

Do you have any accessories attached to the battery, such as cooling fans, subwoofer, driving lights, etc.?

The warm voltage regulator is normal.

Any difference in voltage reading if taken at the alternator tap instead of the battery?

You could take the alt. in to the local parts store and ask them to test it. Maybe it's stuck on full output.

No accessories that I know of...it had an alarm system on it but I disconnected it (I'll check to make sure nothing else is lingering somewhere. So it's really normal for the regulator to be warm even with the car hibernating ?? Wouldn't that draw down the battery over time?

The voltage is the same on the back of the alternator input as the battery itself, the feed comes off the junction block.

I am a quick learner, but I guess need more education on how the regulator/alternator work together. I thought the altenator put out a constant voltage and the regulator adjusted it's own output to the fuse block. So does the regulator adjust the altenator output on one of the 2 wires (Dark Blue) going to/from it?

Ah, you said the regulator was warm with the car sitting idle. I misread that to mean "at idle". Put an accurate voltmeter across the battery a few minutes after shutting off the car. Then check again an hour later. There should be no difference. If there is, you have a "leak".

I suspect that your alternator field leads may be in the wrong orientation. Is the lock tab intact on the alternator field connector? Any chance the field leads have been tapped, switched or rewired? (2 wire connector on alternator)

Here is an informative little text. Note the modification on page 3. http://madelectrical.com/electricaltech/remotevoltagesensing.shtml

Now that I have a better understanding of how all these componets interoperate, I replaced the alternator today. I had checked the wires from the alternator to the regulator and they all matched up to the wire diagram I found on the web.

After getting the new alternator installed and then connecting the battery back up, I was pretty excited to turn the key and check the voltage. To my suprise though the car had an old alarm system installed and it started going off. It disabled the ignition (I can only laugh) and I could not get it to turn off. So I am in the process now of tracing all of the alarm connections and will be ripping it out. Since it has ties into the ignition I plan to take my time and step through it.

If anyone has any real good wiring diagrams for a 68 I would really appreciate them, the ones I am using are a little hard to read.

Since I have never heard a peep from this old alarm system before something tells me I am on the right track and replacing the alternator was a good step. I suspect this alarm system may be the culprit causing the battery drain I was seeing yesterday with the regulator.

Have you checked my website? I have service manuals plus color coded wiring diagrams in the library.

http://thefirstgensite.com

http://thefirstgensite.com/library/electrical/68wir/68wir1.html

http://thefirstgensite.com/library/electrical/68wir/68wir2.html

http://thefirstgensite.com/library/electrical/68wir/68wir3.html

http://thefirstgensite.com/library/electrical/68wir/68wir4.html

and more...

I have a working electrical system !!!!! I got the alarm system disabled, but was still getting occasional high voltage when I had the car on the road, then it would settle down at idle. I ended up replacing the voltage regulator again with a Delco unit and also replaced the external capacitor since I was getting a strange reading on it. While swapping componets out I checked all of my wires again and found the thermo wire to the regulator was changing resistance as I moved it around. I secured the wire with tape and the voltage now normal under all conditions. I'll plan to just change out the wire harness to be safe in the next few weeks.

I want to thank everyone for the help. Thank you Vikki for the wire diagrams, they were a big help in getting the alarm system out of the way. Hopefully I will have some good Fall weather the next few weeks to enjoy the car.

That's cool. Thanks.

You don't need to replace the harness unless you really are concerned about other issues; you can replace the thermo wire. Just match it up with bulk thermo wire at the auto parts store and splice it in with soldered splices and shrink tube. Harnesses are not cheap for the plug and play versions, and though old wire will have some degradation due to oxidation, it should still be serviceable if you replace any damaged wire.