So I have started experiencing a charging issue with my malibu.
Car info
1974 Chevy Malibu Classic
350 SB
AC
Power Steering

So the other day I noticed my Generator Dummy light starting coming on and off. Every time I started the car it got harder and harder to start until I finally ended up having to jump it. I suspected the alternator even though it was new(re-manufactured) Took it in as it has a lifetime warranty and it passed three test runs on the stand. Battery is also brand new. Let it sit on the charger and it started with the same symptoms again. Lights dimming, blinkers slowing etc. From the battery car not running read 12.5 on my meter and about 13.9 running. Right off of the charger without driving the battery read 14.5 while idling. Could the alternator be malfunctioning when it heats up? Could this be a bad cell in the battery issue? I checked all of the wiring and the connections are all good. Is there something that I could be missing? Going to check the battery output again in the morning after sitting over night to see how much of the charge it holds and again while it is running (if it starts in the AM).


Thanks

Ok so I just tested something that I did not check before. I changed the stock radio to a digital display radio. Nothing fancy with tons of watts or anything. Just a 40 dollar Pyle shaft style radio. So here is the thing. with the radio off I get 14.1 at the battery running and will sometimes jump to almost 16. If I disconnect only the digital readout wire I get these same readings with the stereo on. Could this really be the problem???? I would not think the digital readout would take this much away from the alternators charging power?

No way a digital readout would cause this problem. I would bet you have a ground problem. Check all the ground connects. The voltage readings are about right.

From the battery car not running read 12.5 on my meter
Not enough, battery is 1/4 discharged. Should be 12.6--12.7 volts with no load.

and about 13.9 running.
Possibly not enough, depending on RPM. Put the engine at fast idle, and I'd be happier at 14.2.






1. I have no faith in "parts store" alternator testing unless they give you a print-out of:

The maximum voltage with little/no load
The maximum amperage; and the voltage at max amperage
The alternator RPM for max amperage
Amount of diode leakage (ripple; or AC voltage)


Don't get me wrong, it's entirely possible to test an alternator off-the-car, but it has been my experience that MOST off-car testing is done improperly, looking for voltage but not checking amperage or ripple. Voltage is not enough.

2. It'd be best to have a proper test of the entire Starting/Charging System power team; which would include but is not limited to battery load test, starter draw test, alternator output, alt belt condition, and a look at the wiring between all these components. ON-THE-CAR testing is WAY better than hauling one or a few components into a store so a doofus can put them on "the machine" for testing.

3. The on-and-off nature of the generator indicator light potentially signifies an intermittent issue. Have you checked the condition of the two-small-wire plug that snaps into the alternator case? Any other wiring issues?

The plug to the alternator seems to be a good connection. Reading before and after the plug are the same. I still suspect the the alternator as part of if not the problem. I agree that the in store test does not test the same as when it is being used in a vehicle under load and in the heat etc. But it is odd that with the digital read out on the radio disconnected I get a 14.1 reading to the battery and it never drops below that unless I kick on the fan inside then it drops to like 13.9. I will check all of the wiring on the radio again and see if maybe it does not have a good ground. But as of now with the radio off and the wire disconnected that powers the digital read out I have not seen a problem. I will drive it to work today and home again tonight and check the battery voltage when I get home to see if it is charging up. (of course I will have my handy dandy jumper cables).LOL

OK so here is what I found tonight. You mentioned a bad ground. The battery negative is connected to the alternator bracket. So I checked to see if the bracket was a ground point. I connected the positive lead from my tester to the positive on the battery and touched the negative to the bracket which should be a ground point. Guess what. no reading. So I touched the negative to the cable from the battery where it mounts to the bracket. Guess what I get a reading with the battery voltage. I also checked the alternator itself to see if there was ground there and guess what there was. So the bracket where the battery ground is connected to is not ground (it is pretty rusty). So this could be the source to my problem correct? The mounting bolt that mounts the alternator to the bracket has ground should I just relocate it to there instead of trying to run the ground through the bracket to the alternator. If my battery is not grounded to the rest of the car properly this would cause my problem right?

Should I try replacing the ground cable as well? it is pretty old and may even be original?

One other thing that has happened recently before I started having this problem that I just thought about. The buzzer that sounds when the keys are in the ignition and and the door is open stays on when the keys are pulled from the ignition. Could this be related? (A short in the ignition loop) I would not think this would cause a charging issue though?

I don't trust parts store tests either. I just recently had to take an alternator to get it tested to verify what I was reading on my voltmeter was "correct". Turns out that they only test it at 1000 RPM?, and the machine can't spin it fast enough to find a fault at over 2000 RPM. My voltmeter was showing an off the scale reading for 2500 RPM, and they couldn't verify that with the machine because it couldn't rev that high. It tested barely OK at idle for them, but was boiling my battery at higher speeds. Bottom line, that is a VERY basic test, even compared to testing it with a voltmeter.

It couldn't hurt to buy a new battery cable or to find a better ground, plus it's dirt cheap to boot. I'd do it just to make sure those things are right..

Ok so I am still having a problem after all of the above. Checked grounds and wiring seem to be no issues. Last test I ran I sat with my tester on the alternator checking direct output from the alternator. When it first starts up it reads a good 14.2. After running for a bit it will randomly drop to about 13.5. It seems there is an intermittent problem with the alternator after it warms up. When in drive RPM's drop to about 5 hundred and it goes down to 13.6 (this makes sense since the RPM's are lower but should raise back up while driving and raising the RPM's). At fast idle they are at about 8 hundred and that is where I get the intermittent 14.2 dropping to 13.5.

Thanks for all of the help thus far.

does the alt lite glow dimly while running?

No it comes on and off. When it is on is when I am getting a lower output reading on the alternator. When it is cold (engine not warmed up) it is off and I get a strong 14.2 from the alt. but once it warms up I see it come on and off while driving and at fast idle in park.

So I talked to the guy that I normally deal with at the parts store. I told him what was happening and he said "it sounds like the alternators bad" I said yep but your machine said it was good. So I told him I would bring the car in so he could run a test on the alternator in the car. Well he hooked up his tester. Said "well the battery is good" (no dead cells). Then I started the car (glad it had enough juice to start again after the drive over). Well the alternator was not putting out anything according to his tester. It must have taken a complete dump since the last time I had the multimeter on it. He told me to bring it back it when I had a chance and he would replace it. Told him I would be inside in about 5 min. Pulled my box out of my car (I had brought it with me in hopes that this time they would find it bad) pulled the dead unit out took it in and brought the new one out. Hooked it up and drove away. Guess what! No generator light at all. All of my lights and flashers work without dimming or slowing down etc. Car starts right up with no hesitation. It amazing how well a car works when the alternator is doing what it is supposed to. LOL. So far problem solved. Thanks for all of the input and help. I just wish the machine they used to test it originally had the same common sense I had initially when I brought it in and said it did not work. Oh well. Water under the bridge.

this is rare but it happens -the internal voltage regulator normally does NOT go bad gradually. they usually go bad right away and you know it. when the diodes go bad it will test good on the bench, as well, but u will have an electrical draw/drain. a similar issue that also requires Alt. to be repaired/replaced........