Lights flickering (pulsing) when alternator cold and/or with light-moderte load

It actually sounds like the regulator, but I suspect it is integral with your alternator unless you're talking about a 60's era car.

nate

I would be looking 'very' closely at the small ground wire that runs from the battery negative to the fender. If it shows signs of insulation melting, that means the main body ground strap has gone bad or broke. That strap runs from a bell housing bolt up to to body on GM's usually.

Mike

"Rich" wrote: ( XXXX Cadillac X.XL XXX k Miles)

Upon startup and until the engine warms up, I get a pulsing in my headlights; 2-3 times/sec pulse where the headlights get brighter and dimmer. After warmup the pulsing stops.

If I switch on additional loads like my rear defroster, heated seats, etc, the pulsing slows and then stops. Battery voltage at driving speeds is about 14.4-14.5V and at idle is about 13.3V. Outside temperature is 15F. The (120A) alternator was replaced 2 years ago. ______________________________________________

Most auto parts stores will test your alternator at no charge.

The problem could be a failing battery cell. If so, it will draw excessive current from the alternator. Have the battery tested or substitute a friend's battery to see if the condition persists.

Good luck.

Rodan.

OK, here is an update:

First, let me more fully define the equipment:

Now, here is what I have done:

After an overnight, the 'at rest' voltage at the battery terminals was

I removed the battery connections and observed white corrosion deposits on the negative cable. Cleaned both negative and positive cable connections and the battery side terminals.

The negative cable splits at the battery and one wire runs to the block and the other runs to a bolt on the radiator support that runs across the entire front of the car. A smaller wire runs from this frame bolt into a harness.

I measured the voltage between the positive of the battery and the sheet metal bolt and got various voltages between 5-8 volts. Not good.

Positive battery terminal to the engine block is 12.35V. OK.

Removed the battery cables again and measured resistances:

Negative cable to the engine block - 0.5 ohms Negative cable to the frame bolt - 60 ohms and up (varied, obviously having bad connections)

I removed the connections from the car body bolt and cleaned them bright. I observed no corrosion or reason for the high resistance.

Upon reconnection, the resistance at that car body bolt is now about

Restart engine, still have pulsing lights. No change either in pulse frequency or amplitude of bright vs dim.

Removed lower splash shield to get access to the alternator connections. The positive output was tight. I could just barely reach the regulator connection and I wiggled it. It was secure. I could not release it and then reseat the connector without further disassembly.

BTW, changing the alternator with it's internal regulator is a total PITA. When I replaced it a while back it took me 8 hours due to location and access to the fastners. Replacing this alternator again is high on my list of 'never-want-to-do-again' items.

Lastly, I disconnected the negative battery cable and using jumper cables attached another battery to the car. This configuration showed a lower frequency of pulsing and a much lower amplitude of the variation. However, since I have more resistance in the connection to the battery with the jumper cables, I'm not sure what I can conclude.

I reconnected the original battery and then confirmed that the original pulsing problem was still present and unchanged.

I refuse to change the alternator on speculation that it is bad, although I strongly suspect it. I don't really suspect the battery itself, although there was a real difference with a different battery connected with jumper cables.

Unless someone has other ideas for T/S, I guess I will carry some jumper cables with me and pray that when something fails completely that it isn't my wife who needs to deal with it.

OK, experts, thanks for the ideas so far. If anyone has another idea I would appreciate hearing it.

TIA, Rich

Some of those CS alternators are disasters. I had an older Buick that ate them for lunch. Must have replaced a dozen all told, some new oem, some rebuilt at an alternator shop, and some FLAPS. Whether you have a different variant or not, I do not know but I grew to hate these alternators and the engineers who designed them. They basically are too much alternator in too small and poorly ventilated case, and the are known for failure.

Otherwise, I think you are headed in the right direction. Grounds are often the cause for headlights 'flaring'. Rework every ground you can find, and sometimes you may have to add new ones. Read a post the other day where someone found that the wire grounded to the head of a car did not yield a low resistance path to chassis ground. Go figure.

Lastly, if you have the multiple battery cables that GM is so famous for, you may find that they are internally corroded at the terminal. This is very common on some models and can drive you NUTS until you find them.

All the above may have been previously covered, but I cannot see the whole thread. I think your chances of finding the culprit are pretty good if you deal with the three issues above.

Bad alternator. Unless there is a bad connection on the feed from the alternator which is making the voltage to the alternator fluctuate. But I doubt it. You already showed that the battery isn't the problem when you jumpered in another battery and the pulsing remained.

I would run a battery booster cable from the battery negative to the vehicle's body to see if that helps.

The ground you fixed on the smaller black wire from the battery is the secondary body ground. The primary is a wire mesh cable from the bell housing to the body on a GM unless they have changed something in the newer ones.

I know for sure when this mesh cable goes bad, the voltage gauge will pulse with load. The brakes will pulse it, the signals will pulse it, etc.

Mike

Thanks, Mike. I'll try that tomorrow.

I really am beginning to think this problem is a ground somewhere and not the alternator. I suppose the alternator could go bad and cause this condition, but in every other respect the output voltage is fine and it handles any load I put on it.

The other wrinkle is that the engine computer also controls the alternator output. It has a control line into the regulator. There is a good possibility that the computer is actually telling the alternator to pulse.

It's all Gates' fault. Or maybe Bush's. Or both.

Rich

I jumpered the battery negative to first the frame and then to the block. No change, pulsing continues.

There is a cable that runs from the battery neg to both the frame and a second cable that runs to the block. Both are tied at the side connection of the battery. I have checked the resistance of these two cables and found them to be well under 1 ohm. Since I don't have an ulra-low resistance meter, I can't measure much better than this.

I'm starting to look through the wiring schematics to see if there is a particular ground that may be suspect. In particular I will look at the grounds to the engine computer.

Other ideas?

Rich

Y'know, with all the other stuff I see listed that you've tried, has it occurred to you to check the belt's condition and tightness? I had a car misbehaving in a similar fashion once, and after chasing down most of what you seem to have tried, found myself right on the edge of just saying "screw it" and putting a new alt on the beast. Just about that point, I happened to notice that the belt looked a bit ugly. Cranking up the tension a bit stopped the trouble completely. (Then, about three weeks after making a mental note to get a fresh belt, and promptly forgetting about it, the belt broke and wrapped itself around the fan pulley, where it proceeded to beat the everlovin' bejeezus out of the hood liner - Gawd, what a racket!)

Don,

The belt in question is a serpentine with an automatic tentioner. The belt looks in good condition- no cracking, not glazed, etc.

Additionally, the alternator will support any load I can place on it and hold full voltage at the same time. Any other time I've seen a bad belt, the alternator output would decrease with increasing rpm and would not support high loads.

Good thought, though.

Thanks- Rich