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Continued issues with 1968 Olds 442 Charging system,

Perhaps there is an easy answer to this. Recently, I posted about the charging system of this car. Car has been in storage for app 15 yr. I did replace the voltage regulator with a unit from Standard (looks like a good quality part) and a new alternator that is as close to original specs as I could find. The problem is that the charging still seems weak or nonexistent at idle. The GEN light comes on with a faint buzzing, and the interior lights fade a bit. At RPMs slightly higher than idle speed, the light goes off, and I assume the charging system is working properly. Any thoughts on how to correct this?

Im not sure exactly what was changed on this vehicle…but sounds like you have a newer alternator under the hood?

The quick fix would be to simply alter the diameter of the pulley on the alternator shaft. But I would get the specs on what you had…what you installed and then figure out on paper. Also look at the pulley diameters between the two units. One may be smaller than the other…you want to use the smallest one in this instance based on what you said about the Alt light flickering on at idle.


Maybe a bad ground cable from the battery.

Always a possibility… I like to assume if there are ongoing charge issues…the OP made sure of clean tight connections.

But am I asking too much with that one ? LOL thats another topic

Im off to fix a BB Chevy 427 …gotta run


I’ll look into both of those. I have only changed the alternator and voltage regulator (in the charging system). I first changed the regulator and the symptoms were similar to what I have now (apparent OK charging at driving speed) so I thought the alternator might need to be replaced too. The symptoms became a bit better with the new alternator, but the problem still exists. Prior to changing both, the charging of the battery was not happening at all.

Did you notice the pulley diameter between the two alternators? If the new pulley is larger…theres your problem

Assuming clean n tight electrical connections of course. Hell it could be a faulty new voltage regulator…or the reman Alternator ! Do NOT let new parts fool ya…they are bad out o the box more times than you would like to know.

Put a voltmeter on this thing…We want idle voltage at battery…and also at like 2500Rpm…whatchagots?


I would start off by checking the belt. It could be loose or so badly glazed that at low RPms is slips on the pulley.


Here’s the data:

Engine off: 12.48V across battery
Idle Speed: 12.81 V (a bit erratic because the unit seems to be fading in and out of charging mode, but mostly stable at this level)
Higher RPM, likely 2500 or close: 12.8. No change. I was under the impression that when the charging system is working (i.e engine on) the voltage should be somewhere around 13.5.

Another thing I noticed is that the data sticker on the new alternator says that at 6000 RPM, the output is 59A, and at 2000 RPM, the output is 22A. The original shop manual says that new alternators had specs of either 37 or 42A. I am assuming that this would be at high engine speeds, but is it possible that the new alternator is simply underpowered at low RPM?

The lack of significant increased V between engine off and running…I was initially concerned, but it is higher. Does this seem OK?

Thanks for the help.

New belt and it is tight.

The rpm readings on the sticker are for alternator rpm, not engine rpm.

From what you say about the output voltage of the alternator, even if the pulley is the wrong size, the output voltage is too low. You are correct in thinking that the voltage should be at least 13.5 volts and up to around 14.8 volts while the engine is running at around 1,500 RPM. There are a number of things that could cause the low voltage. The voltage regulator, the alternator, or something with the car wiring. Since you say that the trouble is similar as to be fore you made the changes then perhaps the wiring should be checked out. My first check would be to see what the voltage drop is between the alternator output lead and the positive battery post while there is a good load on the system and the engine is running around 1,500 RPM. You hopefully will have less than .3 volts of voltage drop. If you have more than that check all the connections between those points. There should be a fuse in the line. Also check the voltage between the case of the alternator and the negative battery post with a good load on the system. There should be very little voltage drop if the grounding is good. The wiring between the regulator and alternator is another area to check.

You say you hear some buzzing at idle speed. This could be a clue and mean there is ripple voltage coming from the alternator which may have some bad diodes inside it and that would cause a lower than normal output voltage. Check for AC ripple using the meter in the AC voltage mode across the battery and the engine at idle speed. You should see less than .1 volt of AC ripple voltage. If there is more then you most likely have a damaged alternator. When making this test you need to know if your meter blocks DC in the AC mode. If you see a voltage reading while in the AC mode across the battery, or any battery, then you would have to add a series blocking capacitor in one of your probe leads in order to block the DC component. About a 2 microfarad capacitor should work for that.

Thanks, Cougar-

Great, detailed advice.

One thing I may do is simply to swap the alternator for the original and re-check the voltage at 1500 or so. Before I put in the new alternator, I did see voltage of around 13.5 or so when the car was running, and then it went back to about 12.3 or thereabouts when the engine is off. Maybe I got a bad alternator? I can’t recall if this was before or after replacing the voltage regulator, or both. I still have the old alternator sitting there.

The buzzing seems to be the GEN warning light itself.

I’ll keep working.

Please help with this question. To check the voltage drop between the alternator output lead and the positive battery terminal, what exactly need I do? It is just to connect the voltmeter between the alternator terminal that goes to the battery (labeled BAT I believe, and the + terminal? Do I need to remove the wire from the alternator BAT terminal first? I’m a bit of a novice at this, obviously.

Thank you!!

After testing the alternator output cable measure the voltage on the “F” (field) terminal on the back of the alternator, there should be a 12 volt supply from the regulator when the battery voltage is low.

To perform a voltage drop test place your voltmeter leads on each end of the alternator output circuit, the positive lead on the “battery” stud on the alternator and the negative lead on the positive battery post with the engine running. The voltmeter will show the loss in the circuit, should be about .2 to .3 volts.

Or you can start the engine, measure the battery voltage and then the alternator output voltage and do the math, the difference should be .2 to .3 volts. If you measure 18 volts at the alternator, you have a problem in the cable between the alternator and battery.

Thanks for all of the help.

Things got curiouser and curiouser.

I put the old alternator in. Started the car. Same symptoms. Voltage is about 12.3 with car off, and running at any RPM.

Was playing with measuring the voltage from the alternator, assuming I was to do as Nevada_545 said, with the + lead of the meter on the BAT terminal on the alternator, and the (-) lead of the meter on the battery (+) terminal. The measurement was hard to interpret…more like the meter didn’t know what was going on. The reading was a bit jumpy but mostly just a 1 on the left hand side of the display, as if something was really wrong. So, I assumed something was. Usually the readings are right justified.

But then I decided to press the plug end of the wiring harness that goes into the voltage regulator hard, as if I was trying to plug it in and struggling, in case the contacts were not good, and then the voltage at idle jumped up to about 16.3. When I revved the engine, it jumped back to about 13.5 or so as I would expect. However, at idle, the GEN light still comes on, with the buzzing. Funny thing, I turned on the lights, and while revving the engine, they seemed normal, but when the engine dropped back to idle, they got brighter (presumably due to the increased voltage).

I"m going to obtain a new wiring harness and start from there and hope that helps.

I’ll keep at it. Hopefully it’ll be corrected soon, as it is almost that time of the year to put the top down and enjoy the car.

Thanks again to everyone for the assistance.


Good advice by @Cougar above. The voltage output the alternator depends on how well the battery is charged. With a fully charged battery a good alternator might only put out 13.5 volts, and that would be independent of the engine rpm. And it might put out 15 volts at idle rpm if the battery was almost depleted of charge. that’s what the voltage regular does, adjust the alternator output for the engine rpm and for what is needed to charge the battery. Even if your battery is fully charged, the voltages you are citing are lower than what I get on my Corolla. I get at least 13.5 volts, and up to 15 volts out of the alternator, depending mostly on the current battery charge level.

For the charging to work properly you have to have very low resistance between the alternator and the battery. So that’s the first place to look. By low resistance I mean on the order of 1/1000 ohm. This applies equally to both the positive connection, and the ground connection. Ohm meters won’t read that low accurately so you have to measure it by a voltage drop test instead; e.g. 50 amps across 1/1000 ohm would measure 0.05 volt. 1/20th of a volt, which volt meters can easily measure accurately.

Good for you for getting your 442 back on the road. Shell oil thanks you too!! …lol

One other idea, you might ask a good auto parts store if they have a test fixture that can test your alternator/VR combination. That might prove worthwhile to figure out what’s going on.

Do you have a gadget that measures high currents, like up to 100 amps? There are inexpensive versions that just use a magnet to measure the magnetic field from the current in the wire that work pretty well. I’ve used mine quite often, I bought it at Sears I think, years ago, cost less than $10 at the time. That’s a pretty useful tool for problems like this.

Edit: BTW, if I were doing something like this I’d use an alternator that has the VR inside. I wouldn’t mess with a separate VR unit. It might require some modification to the wiring harness is all. Are you able to post a diagram of the schematic for the alternator/VR/battery for your car?

Edit: Didn’t that car have something like a 7 liter engine?

Please excuse my post. My memory has again failed me.

Don’t remove any parts for bench testing and you don’t need an amp meter, just measure the voltage on the battery and field terminals on the alternator when running and post the readings.

I’ll try to tinker more today and post additional information. Thanks to you all.