1983 chevy caprice battery goes dead

My kid has a 1983 caprice that the battery goes dead. originally we thought alternator was bad. when we put voltmeter on battery (12volts at rest) and
started car voltage dropped. we were expecting 13volts or so. we have taken alternator in twice, two different shops and both said alternator checked out o.k. upon further examination we found one of the spade wires that go into a connector that attaches to the alternator bad. It would slip out of the plastic connector. we were able to repair this connector (supply of field voltage?) and then started car and voltage this time did not drop and it read about 12.4 volts. we went to lunch and came back about 1hr later and car started with no problem. (well almost no problem it is a 1983). voltage read just a little over 12volts but it was not dropping below. (unless headlights were turned on and then 11.7volts). before my kids car would not start even after 1hr of just sitting.
my kid tried starting car next day and battery completly dead.
my thoughts are something is staying on and draining battery. I think to troubleshoot problem we need to get car started and let it run for a little while charging battery. then turn car off and then remove neg cable to battery and put meter in between to see if current is being drawn. if so start pulling fuses and see if we can find culprit.
battery was replaced about 5 months ago. he pulled both alternator and battery out and the parts store said both check out o.k. We even got a second opinion on the alternator.
any other thoughts on my kids caprice classic woes out there? my kid lives a little way out of town and works 6 to 7 days a week. so our trouble shooting time is somewhat limited. any input would be helpful.
thanks rod
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Look.. Check the battery draw when the car is not running. Make sure some circuit is not draining the battery. You should not draw more than maybe 50 milliamperes or so.
If you are drawing considerably more, then you have a defective circuit.
Possibly, if not probably, your old battery is toast by all this falderal..
Dont just guess and replace.. Diagnose and repair.
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yes i agree on not guessing. it would of been easy to just buy another altenator and still have the same trouble. I wasn't sure on what kind of draw was acceptable when car was not running. thank-you for the info.
rod
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Have you checked the battery? How old is it? In spite of being able to hold 12V, it may not have the power for anything else and it will not take a charge. If more that four years old, I'd replace it. If less, I'd try it in another car to see how it performs. Have you tried putting a charger on it?
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He took battery in and they said it checked o.k. It is only 4 or 5 months old. no have not put it on charger. thanks rod
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This is insufficient to charge the battery.

Clearly insufficient, shows that there is low alternator output. This could be a wiring fault.

Well, if the battery was not charging, that is not surprising.

Either self discharge due to a bad cell, or there is a parasitic draw that is discharging the already very badly charged battery.
1. Put the battery on a proper charger, and charge it fully. 2. Measure the battery voltage, with it disconnected. Record this value. 3. Leave the battery sit for 12 hours, DISCONNECTED, and then measure the (open) terminal voltage. It should be almost exactly the same voltage as in step 2, above. If it is about 1 to 2 volts less, the battery is defective. 4. Connect the CHARGED battery to the vehicle, with a properly connected amp meter. Allow the vehicle to sit, doors closed, all lights off, everything off (if the hood has a light, that is lit, remove the bulb for this test. Measure the draw after 30 minutes, if it is more than 50 milliammps (0.05 amps) then you have a high parasitic draw, find and correct this problem.

If will not charge the battery if it is only putting out 12 volts. You need between 13.6 adn 14.2 volts to properly charge the battery, and that voltage would have to be maintained for considerable time (hours) if the battery is in a state of low charge. You need a proper battery charger.

Making sure to:
1. Wait between 20 and 30 minutes, 2. Ensure that all devices and lights (including the hood trouble light) are off, 3. and then monitor the draw. If more than 50 milliamps, then there is a problem. 4. Remember: if you open the door, the dome light, and other systems in most cars, will result in a large current draw, possibly damaging the meter. Disable the door switch prior to making these tests.

Just because the battery was replaced five months ago doesn't mean it has not failed. Also, it is clear from your voltage readings that the battery is NOT charged properly. Put a proper battery charger on the vehicle and fully charge the batter as described above. Run the 12 hour sitting test!

Get him a loaner car so you can properly diagnose the problem. That will help greatly. Measure voltages at the alternator to see if the alternator is in fact putting out the proper voltage.
Personally, I think both the alternator and the battery are probably defective, but the wiring could also be an issue. (Don't say: we checked the alternator, that and $5 will get coffee and a donut at Dunkin...)

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wrote:

thanks for the input.
as far as measuring voltage at the alternator that may be a tall order. from what i remember the lead connector is difficult to get to when alternator is installed. however I did measure voltage from ground to positve of battery and then from ground to lead that attatches to alternator and obtained same voltage. (this done when car at idle and alternator not installed). its just a short piece of wire.
What is the resoning behind waiting 20 to 30 minutes? if there is a parasitic draw wouldn't it happen immediatly? sorry electronics background not mechanic background.
I agree it would look like alternator and/or battery is defective. but alternator was tested by 2 different parts stores. keeping in mind that parts stores are there to make money. so i would assume that if there was an issue with alternator they would have sold him a new one. and battery the same.
what kind of tips are you leaving at dunkin donuts? or am i out of touch? haven't been to a donut shop in years.
thanks rod
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Sometimes you have to do the impossible. Even runnign a temp test lead.

If the alternator is not installed, then the test is meaningless.

Computers, ECMs and other similar stuff may not 'go to sleep' for a while.

Never... Personally, I think the alternator is toast.

Depends on how cute the girl behind the counter is, and how she chats me up.

Coffee at Dunkin is not that bad, just skip the silly donuts!

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If it were my vehicle I would take it to a shop, that has the proper equipment and the trained techs, to have the problem analyzed and the fault corrected, rather than the hit or miss route you have been following.

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A fully charged battery should read 12.67 volts. Normal charging system voltage on that car is 14.5 volts. (OEM voltage regulators did have some temperature compensation WRT charging voltage)
There are three connections on your alternator; 1) stud and nut is the alternator output terminal, it connects directly to the battery. 2) larger red wire at two cavity plug is the voltage sense wire, it also connects directly to the battery. 3) smaller (usually) brown wire is the turn on signal, its job is to signal the voltage regulator to wake up and function, this circuit is hot only when the ignition key is 'on'
(field current is supplied internally to the alternator thru the diode trio which taps current off of one half of the stator)
If indeed the alternator is not the problem, you are missing voltage on one of the above three mentioned circuits. Voltage available and voltage drop tests will find the problem.
Both red wires are protected by fusible links located in the harness that goes to the starter motor.
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wrote:

Good advice. Some more advice...if you do have to change out the alternator, get a good one...perhaps from a friendly local alternator shop or a top quality unit from a FLAPS. Some franchise stores sell some pretty sorry rebuilt alternators with "lifetime" guarantees.
I have replaced a bunch of them.
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