Alternator randomly stopped charging when I was out driving. Got home running on battery. Figured it was a bad voltage regulator on my 8 year old alternator. The next morning it was fine. I bought another AC Delco alternator from Rockauto. I also put in a new battery. It was fine for about a week so I figured I had the problem fixed.

Then it happened again. Same problem. I looked at the wiring plug and tweeked the connectors on the plug and alternator to make sure I had a good connection. It worked fine for a few days and then it happened again. I looked for loose wires and did not find any.

Has anyone had this problem?

 

Does the Choke light come on when you turn the key on w engine off, then go out after it starts? Was the light on while the alt was failed?

 

A good place to start would be to check and then clean and tighten the engine-to-frame/chassis ground connections as well as the battery cables.

 

Sofa, I don't remember a light coming on but the volt meter dropped way down because it was running off just the battery. The next day I went out to diagnose and it worked fine. Until it did it again.

 

Ironwill, thanks. I'll check those. I also ordered a new alternator pigtail. It's gotta be something simple. Just have to find it.

 

The alt gets its "start" signal through the bulb: key on puts 12V on one side of the bulb, and the regulator inside the alt is on the other side, waiting for that voltage to be told "OK charge now". If the bulb is burned out, the alt will never know that it's supposed to charge, and will only do so more or less by accident.

Replace the bulb first. Then go from there.

 

Thanks, SOFA. Is it possible to just provide a different power wire to the voltage regulator?

 

Not really. Not sure how hacking up the car's wiring could possibly be a better "solution" than changing a burned-out light bulb, in any case. Jerry-rigging the alt wiring is not even A Good Idea to begin with, let alone "better" than a moment of simple maintenance.

 

And you MUST use a bulb, not an LED.

 

Thanks Sofa and No Emissions. I was only thinking about trying a different power wire for troubleshooting. I'll check the bulb and replace it.

 

I checked and, sure enough, the bulb is not working. I'll swap the bulb this weekend.

Seems like a strange setup that a blown light bulb can make you walk. Thanks engineers.....

 

Yep. Archaic design...

 

Which alternator is this? If a CS series with a 4-terminal connector, can wire a +12 V ignition switched source to the F terminal. This will allow the alternator to charge even when the bulb circuit fails.

The issue with the bulb circuit is that it may not be a burned out bulb. It may be the contacts between the bulb socket and the flex circuit (in the cluster). Or the contacts between the dash harness and the flex circuit.

So don't be surprised if the bulb is good.

RBob.

 

Yup, could be that. Could even be that the space aliens got bored with creating crop circles and UFO sightings and instead decided to infest your car instead, just for a little spice in their life.

AFAICR an 87 would have had the same 10SI as had been in use since the late 60s. Butt I don't pretend to be an expert.

Start with the simple stuff first. Move on to all that other "could be this, could be that" AFTER the simple obvious things have been ruled out.

 

Yes, it could be any number of things. But at the same time the entire drivetrain has been swapped. From a 2.8l MPFI to a 350 SBC. So who knows which alternator is installed.

RBob.

 

My setup is a serpentine belt system from a 1990 Camaro. The alternator plug matched the existing 1987 V6 factory wiring harness. It has been like this for 13 years.

The strange thing is when I removed the instrument cluster, I could not find a bulb for an ALT or BATT light,,,,or even a place for one. It does have a factory volt meter. Is it possible that it does not have a factory idiot light since it has a factory volt meter?

Also the alternator was charging fine with the engine running and the cluster removed. The signal wire to the voltage regulator showed 12 volts.

I did change the wiring pigtail to the alternator today and also an extra body ground to the battery.

I guess I will see if this fixes the problem.

 

The cars with voltmeters didn't get the BAT bulb indicator. I wasn't sure which one an '87 Firebird would have. In this case the alternator plug should have IGN+ switched power to the F terminal. The terminal markers are molded into the plug. This is what makes the alternator charge. Which should be a CS-130?

The I or L terminal would be for a bulb if it was used.

The S terminal was typically wired to the starter battery lug. In order to sense the voltage at a better location.

On a '92, which should be similar to a '90, not sure about an '87, looks like this:


RBob.

 

Thanks RBob. I appreciate it.

I took it out for a drive and so far so good.

I guess I have a good backup alternator because that wasn't the problem after all.

 

Thanks! Never knew that.

 

UPDATE---Well, it was fine for two weeks then it happened again last night. Gotta be a loose connection somewhere.

Of course, it happened last night at midnight on the way home from work and I did not have my voltmeter with me to diagnose which wire was not working. I will have it with me from now on. I thought I had it fixed.

 

I finally got a chance to investigate while the alternator was not charging. When it is not charging, there is no voltage at the "L" wire on the connector...checked by probing the wire. Also, at that time, the voltmeter showed it to not be charging. Removed positive battery post cable and the car died.

When it decides to work correctly, there is voltage on all three wires of the pigtail connector. "S", "F", and "L". The "P" position is not used. This is a new problem. It has been working perfect for 13 years.

 

OK, dug out some '87 wiring diagrams, not sure if correct. But not much else to go with.

The S terminal is a sense wire. Ends up at the battery + via a fusible link at the starter 'big' lug. Should always have power. Won't affect changing, but does affect general vehicle system voltage.

The P terminal is pulse, only used on diesel engines for a tachometer.

So, the L & F terminals are the key here. They each get power at key-on from different locations. And, different wiring connectors.

Only one or the other is required for the alternator to charge the battery. So something is going on here.

Power for the F terminal (field) is from the C/H-Fan fuse. Runs through the C221 connector (near ECM, clear), and joins the EFI harness out the passenger side. It also supplies power to the coolant fan relay coil. Then on to the alternator F terminal. There is a splice in the interior and another under the hood for this wire.

Power for the L terminal (lamp) is from the GAGES fuse. This power runs a convoluted path into and out of the cluster printed circuit. Apparently there are 3 different clusters that were used. One used a hidden bulb (digital), another used an observable bulb (indicator cluster), and another used a resistor (gauges cluster).

This feed goes through the C100 main bulk-head connector.

So, bottom line, key-on, engine-off, all three alternator connector terminals should show battery power. Simple as that. If any, I would work on the F terminal power feed first. It is a more straight forward feed to the alternator.

RBob.

 

Also Note that Two Different Style Voltage Regulators have been being used in our alternators since the CS-130 Models started:

 

Thanks for the input guys. I really appreciate it.

When the alternator is working correctly, all three wires have 12+ volts. It seems that none of the wires have a resistor. When the alternator is not charging, there is no power only to the L wire and the gauge is reading low because it is only running on battery. But the F and S still have power. Apparently, my problem is with the L wire somewhere. My car has a voltmeter instead of an idiot light. The alternator charged fine with the instrument cluster completely removed. Seems strange because I thought one of the wires ran through the voltmeter.

This is just an occasional random problem with my original 36 year old wiring. I guess my question is, do I need the L wire?

 

OK, if there is voltage at the F terminal (while connected to the alternator), and the engine is running (alt spinning), it must charge. If not the alternator is bad.

As you discovered, even with the cluster removed the alternator was at one point charging the battery. This is because of the F terminal being powered. The L terminal is in this case somewhat redundant. It can be used as a alternator dead indicator, but on a gauges dash it isn't.

Rockauto lists the same alternator for '87 - '92 Camaros. And look at the '92 wiring diagram I posted above. Nothing on the L terminal, not needed.

Next time it won't charge disconnect the 4-position terminal and run a wire between terminal F on the alternator, and battery +. That should/must kick the alt into charge mode.

RBob.

 

Thanks again RBob for all of your help.

Today I disconnected the L wire from where I spliced in the new pigtail, just to try to diagnose things. Took it for a 20 mile drive after that and everything worked as it should. It had been hooked up to the factory harness for the last 13 years.