On my 67 400 convertible I have been having a problem. I have a new battery and after a few times out yesterday, the car would not start. I took off the alternator and had it load tested - 15 volts. I changed the electrical plug in the back as it looked and seemed a little loose and charged the battery back up. Today the exact same scenario, out of a few times and dead. Had the battery tested and it was fine. I put my volt meter back on and it read 12 volts and when I cranked it it dropped to 3-4 volts. I jumped the car and the battery recovered to 12 BUT never went above 12 so it is not getting the charge for the alternator. So, I changed the voltage regulator and jumped the car AGAIN and the battery was charging at 13 volts at idle and 13.2 at throttle. The 13-13.2 seemed to be a little low for the charge rate. Does anyone know what your charge rate is or what it should be. It fired right up after a long drive without an external charge. Hopefully this resolved the issue!

mine charges at 14-14.5v, about 13.5 without alternator powered on.

I'm not quite sure what you mean by "without alternator powered on." Nevertheless, your charging over 1 volt higher than I am. I can't imagine where I am losing the power. In your opinion, is 13-13.2 sufficient to charge and not leave me stranded? Do you have any other places I can check? The test on the alternator showed 15 volt output that was a needle bouncing, I have a digital readout on mine. Thanks

If your voltage regulator is working, immediately after starting or on low battery condition the alternator will be charging at 13.5 to 15.2 volts. You can check the voltage at the battery lug of the alternator, and again at the battery, to see if you have voltage drop. You need more than 13.5 volts to charge the battery.

After the battery is fully charged, the alternator will stop charging (stock design). Then the battery voltage will be lower, and should be no lower than 13.5 volts. That's nominal voltage, anything lower and you may be stranded. 12 volts is a dead battery.

Do you have any idea where I am losing volts? Alternator is good, regulator is good, battery was manufctured 6 years ago but was tested and is good!

Whoa, first things first, that battery is on borrowed time. Replace it before you do anything else. You mentioned in your first post that the voltage dropped to around 3 or 4 volts. Load testing the battery, it should not drop below 10 volts or so. A battery at 12 volts is 50% discharged, each of the six cells has a capacity of 2.1 volts giving you 12.6 volts for a battery in good condition. I have a brand new alternator and new voltage regulator(external) and it maintains about 13.75 volts at all times, no load, lights on, blower on, stereo blaring so save yourself another tow call and replace it!!!!

P.S. triple A is 60 bucks a year

Will changing my battery change my charge rate? Since the battery only takes what it needs should I assume the ability of thay battery to fully charge ia lost?

No, but the current battery may have a bad or intermittently shorted cell and that would cause erroneous readings at the battery. Also, I forgot to mention you should check for a parasitic draw on the system.

Get a test light. With the car off and nothing on (courtesy lights, radio etc.) Remove the negative cable from the battery. connect the test light to the cable end, touch the probe to the negative terminal of the battery. If the light comes on or glows, you have a draw in the system (which can be a alternator or regulator problem even if they are working properly) No light is what you are looking for.

Hope this helps!

Excellent Advice, and I concur!

First post said battery was "new", I guess definition varies.

Hehe, yup, new is subject to interpretation!

Just messing with ya Peter!

I was just shown the tip listed above about the test light. Works like a charm. If the light does light up, you can begin to pull fuses, as soon as you pull the fuse linked to the "problem" the test light will go out. However you must also keep doors closed or keep the dome light pin switches pushed in as they will cause an open circuit.

I actually was able to track my "draw" to the tail lights, one of them was not grounding out properly, as soon as I wiggled the socket the test light went out...

a 6 yr old battery is not new...its past its life...
I had a 60 mo Die Hard , it lasted actually 6 yrs...then I replaced it 3.5 yrs ago with a 36 mo battery...expecting it to go out any day...had it checked last mo, still good...but it wont be long now...

get a new battery!

Here's a horror story that sounds much like the problem discussed here.

I have been having a problem with slow cranking at the starter after a couple hours of driving and with the battery going dead if the car is unused for a few days. Sometimes the car would start after an hour's rest, sometimes it would not. Sometimes it would start with a jump, sometimes it would not.
The alternator tested good at many, many tests, so I have not yet replaced it. I will have to replace it, since it is the ONLY thing that is not new. I have replaced the starter, the battery, the ignition switch, the neutral safety switch and today, after giving up on doing it piece by piece I finished installing a brand new wiring harness, which took a few days.
I changed the battery, started the goddang thing and let it run for almost an hour, shut it off and to my dismay, the problem persisted: at the second try the starter would crank really slow, then start clicking. No start.
Before I plop down more money to replace the alternator I registered here to see if I could find some advice. The testlight method suggested above sounds really practical, I shall run it tomorrow.

Also, the alternator has R and F terminals, besides battery and ground. I connected it the way my new harness said, with a brown wire left hanging, as it was before. The R terminal is not plugged to anything. A red wire from the battery went to the F terminal.
I did this without fully comprehending the function of the terminals, and the charging system tested good on my tester.

Any advice at all will be greatly appreciated, I'm confident that if I will find the answer to that really annoying bug it will be in these forums.

Mac.

What model of alternator do you have, and is your car equipped with an external voltage regulator? It sounds like you have the field lead connected to an unswitched circuit, which WILL drain your battery.

The hot/slow cranking is a separate issue, quite common, due to heat and degradation of the starter, solenoid, and/or battery cables.

See http://www.hartin.com/alt.htm for some basic information. See http://thefirstgensite.com/library/electrical/68wir/68wir1.html for the althernator wiring diagram for a 1968 Firebird.

Thanks for the quick reply, Vicky.
I am aware of the slow cranking due to heat and I put all kinds of heat protection around the starter when I replaced it, to reduce that possibility. It's got an asbestos wrap-around cover and a sheet metal shield clamped between the starter and exhaust manifold. I must regretfully say that I hardly noticed the difference.
I will come back to you tomorrow with pictures and numbers from the alternator.
Should I post my issue as a separate topic?
The car originally had an external regulator, which was completely ignored by the diagrams that came with my new wiring harness. I did not put it back on. The car is behaving exactly the same with the new harness, without the regulator.
All other things are working perfectly, I have lights that had not been working before and new switches all over, but the main cause thet made me replace the harness is still there. That's pretty frustrating.

What type of harness do you have? You've made a lot of changes without resolving the issue, so it will take some interactive troubleshooting to find the root cause.

If you have an internally regulated alternator like the 10SI (1969 with A/C) then the regulator's internal diode may be bad.

If you have an externally regulated alternator like the 10DN (most non-A/C 67-69), and you did not reinstall the regulator, do you have the regulator jumper block installed?

Is your alternator actually charging? Take a voltage reading with the engine off, then another at the same point (battery positive or horn relay) with the engine running. The voltage when off should be 12.6v or above, and running should be 14.3v or above.

What about battery cables....doesn't look like they were mentioned.

You do, or do not have an external voltage regulator?

Yup, new battery cables, as well as new and quite overkill ground straps all around. I'm fairly certain now that the problem resides with the alternator wiring.
In a moment I will upload pictures of the whole thing.
I'd like to know if it's even the right alternator for that car, as the problem was there when I bought it. I was even warned by the previous owner that the battery was getting drained from somewhere. He did not know what the problem was and I replaced part after part overlooking the alternator because it tests good.

Nope, at the time the car is without the external VR. I didn't hook it back up because the diagrams of the new harness overlook it, so I am not sure how to hook it up.
Pictures in a few minutes.

Alternators can charge/test good and still have a parasitic drain on the battery, have you done the test light procedure yet?

If there is a wire from the field terminal straight back to battery, it's going to drain. Once we can see what you have we can help you find a way to fix it.

Ok, I'm back with pictures.
This is the alternator with the two wires disconnected. One of them was not connected to begin with before I rewired the car.



Alternator top view and side view. There are no tags attached to it, only the numbers stamped on top.





These are pictures of the diagram that came with the new harness. I blurred out the brand to avoid any copyright infringement issues.





Finally, these are the components that came with the old wiring. I have to confess that I have no clue what the white one is. The wires that went to the alternator with the old wiring are the blue and black/white ones that attach to the regulator's first two terminals.





If I need to take more pics to clarify anything else, let me know.

I think I have a good location on the source of the problem now that I know a little more about the wires behind the alternator, but I will still do that test tomorrow, if the battery is still drained after unplugging the F terminal on the alternator.
Hopefully it will be that and someone will suggest the course of action.

If you read the last page of your instructions, you will see that it talks about an INTERNALLY regulated alternator, and a one wire alternator. You don't have either.

You can change out your alternator for a '69-mid 70s internally regulated 10SI from any auto parts store and use the wiring you just bought.

I have no idea how long that alternator has been on the car. I bought it 3 years ago and the problem came and went, but I was indeed warned about it by the previous owner, who never suspected the alternator. I didn't either, until now.
I will do as you suggest, replace the alternator.
Two questions, though:
Is that alternator the right one for the car?
Is there even a way to hook that one up right or would you suspect it was never hooked up the right way, so it kept draining the battery?
The car is a 68 400 automatic.
I appreciate the help.

The alternator is correct for the car, with the original harness and voltage regulator. To work properly, all the wires would have to be connected as the factory had them. You can't do that with the replacement harness you have without modifying it. Since alternators are cheaper than harnesses and the 10SI will bolt right in, it's the easy-good fix.

Without seeing what you had before you replaced the wiring, it's hard to tell what was wrong. I've worked on cars that had some incredible workarounds done that worked somewhat, but never quite right.

New alternator it is, then.
I really appreciate the help, I'll let you know how it went.

Cheers.