4-wire alternator wiring question...

[67 Burb]

I'm using a volt meter rather than an indicator light on my CS alternator, so I just ran a wire from the ignition to the "F" which shows as the "I" (for ignition) connection on one of your diagrams. Full 12V to there, so no resistor is needed on that connection.
Got that info from a buddy who has an auto electric shop.

[dmjlambert]

Yes, I agree the S wire not used in their application at American Auto Wire seems weird to me. I liked their article for the information they gave about the F/I terminal, but the adapter they propose I don't know about. I like the ACDelco adapter, it just makes more sense to me, pun intended.

It seems there is no single source of really good and complete information on this subject. I guess it is because there are so many ways to do this, so many different parts to use, and we're attempting to use the incorrect parts for our trucks. There was no CS alternator when our truck was designed. And there were less electrical demands on the trucks the way they came from the factory.

The recommendation is to hook up the sense wire at a junction point a few feet from the alternator. In the stock harness this would be at the point the alternator main wire splits and goes to the battery and goes to the cab fuse panel.

Feet or inches of wire have different voltage drops when there is a lot of current flowing vs when the battery is just being kept charged. How much of a difference it will make in an average installation, I don't know. In any case, I am guessing hooking up a sense wire a couple of inches away from the alternator, or a few feet from the alternator, would not have any impact on whether the alternator gets burned out prematurely. I could be wrong. I have not seen posts from people admitting they learned their lesson about having a short sense wire.

If you have 4 feet of 10 gauge wire on the output of the alternator, that is .004 ohms resistance. Suppose you have accessories that draw 80 amps of current. You get 0.32 volts of voltage drop on that wire. The sense wire, if connected at that point, can tell that the alternator needs to put out a lot of current, and it adjusts the alternator output appropriately. So, it is true there is not much resistance and it seems you shouldn't worry about it, but in theory when you're dealing with a lot of amps the very small resistances make a difference. If the sense wire is connected right at the alternator output, it will not get a chance to sense the current draw as well.

[nikwho]

Originally Posted by 67 Burb

I'm using a volt meter rather than an indicator light on my CS alternator, so I just ran a wire from the ignition to the "F" which shows as the "I" (for ignition) connection on one of your diagrams. Full 12V to there, so no resistor is needed on that connection.
Got that info from a buddy who has an auto electric shop.

I too am using a voltmeter, and have no dash indicator light. However, from everything that I have read, hooking 12v to your I/F has a 50/50 chance of either working fine, or frying the voltage regulator. I REALLY don't want to buy a 4th alternator. Did you do any testing to ensure that yours was the proper configuration, or do you reckon that you just got lucky?

Nik

[nikwho]

Originally Posted by dmjlambert

Yes, I agree the S wire not used in their application at American Auto Wire seems weird to me. I liked their article for the information they gave about the F/I terminal, but the adapter they propose I don't know about. I like the ACDelco adapter, it just makes more sense to me, pun intended.

It seems there is no single source of really good and complete information on this subject. I guess it is because there are so many ways to do this, so many different parts to use, and we're attempting to use the incorrect parts for our trucks. There was no CS alternator when our truck was designed. And there were less electrical demands on the trucks they way they came from the factory.

The recommendation is to hook up the sense wire at a junction point a few feet from the alternator. In the stock harness this would be at the point the alternator main wire splits and goes to the battery and goes to the cab fuse panel.

Feet or inches of wire have different voltage drops when there is a lot of current flowing vs when the battery is just being kept charged. How much of a difference it will make in an average installation, I don't know. In any case, I am guessing hooking up a sense wire a couple of inches away from the alternator, or a few feet from the alternator, would not have any impact on whether the alternator gets burned out prematurely. I could be wrong. I have not seen posts from people admitting they learned their lesson about having a short sense wire.

If you have 4 feet of 10 gauge wire on the output of the alternator, that is .004 ohms resistance. Suppose you have accessories that draw 80 amps of current. You get 0.32 volts of voltage drop on that wire. The sense wire, if connected at that point, can tell that the alternator needs to put out a lot of current, and it adjusts the alternator output appropriately. So, it is true there is not much resistance and it seems you shouldn't worry about it, but in theory when you're dealing with a lot of amps the very small resistances make a difference. If the sense wire is connected right at the alternator output, it will not get a chance to sense the current draw as well.

I've read up on this more, as well. Seems that there is definitely merit to the remote sense wire. I am wanting to not butcher my wire harness more than needed. It seems to me that the voltage drop would be read by the sensor wire, if ran to the positive terminal of the battery. Ill also take another look at my wire harness diagram, and see if there is another place that is more ideal to tie in the sensor wire.

[67 Burb]

Originally Posted by nikwho

I too am using a voltmeter, and have no dash indicator light. However, from everything that I have read, hooking 12v to your I/F has a 50/50 chance of either working fine, or frying the voltage regulator. I REALLY don't want to buy a 4th alternator. Did you do any testing to ensure that yours was the proper configuration, or do you reckon that you just got lucky?

Nik

Here's the info my buddy sent me. Notice in the second diagram it mentions that "The switched 12Volts may be applied directly to the "I" terminal." On my alternator there is both an "I" and "F" shown for the same terminal, but only an "F" on the plug.

[nikwho]

Man, so, according to your data, post '87 alternators should be able to be excited by the "I" terminal. My only reservation on this, is what if that particular CS130 alternator is wired with a regulator with the "F" terminal... Ugh... Im conflicted, because it sounds like this would most likely work. Buy, the info provided by dmjlambert suggests a mere 50% chance of this working, without cooking the regulator! Man oh man.

[67 Burb]

My alternator came off of a 1989 Caprice and it seems to be working fine with only the F wire connected, but if there are different configurations in other years, I don't know. You would have to get an expert's opinion on that.

[nikwho]

My alternator is off of an '89 Blazer... I suspect that it would likely work, but I'd sure hate to be posting here in a couple of days telling you all about the 4th alternator that I had to buy! LOL. I do appreciate your info!

Nik

[dmjlambert]

Originally Posted by nikwho

Man, so, according to your data, post '87 alternators should be able to be excited by the "I" terminal. My only reservation on this, is what if that particular CS130 alternator is wired with a regulator with the "F" terminal... Ugh... Im conflicted, because it sounds like this would most likely work. Buy, the info provided by dmjlambert suggests a mere 50% chance of this working, without cooking the regulator! Man oh man.

Well I'm not an expert on this. It could be 90% of the alternators have the I terminal in that position, and just a small number were made with F terminals. In that case your chances of winning the alternator wiring lottery would be in your favor. The folks who know this sort of thing as fact would probably just wonder why do you need to know, just use the correct alternator for your year/make/model. But we want to hack on our trucks!

[nikwho]

Haha! So true!

[nikwho]

Because of my nature, part of me wants to try this, as it would be such a simple install. And, perhaps a bit exciting to play the "alternator lottery"! I also wonder if wiring it one way or the other would provide greater longevity.

[dmjlambert]

If you're going to have that kind of nature, open up that alternator and research the part number of the regulator and figure out how to verify if it's a PLIS or PLFS type. If you encounter a PLFS regulator in there, you can probably swap it for a PLIS regulator, and then you'd be all set and can proceed.

It's my nature to look for the safest way that works. I'm rather satisfied with the documentation that 67 Burb got from his friend, it looks like solid info there about the L terminal. When reading that information about the I terminal, that sounds OK also until you think about how that terminal position could be for F and we don't know how to wire that, and it certainly sounds like we shouldn't put 12V on it. The American Auto Wire article says the F pin is an output to provide field duty cycle information to the vehicles ECU. That same article says "Be forewarned!!!" about using the F/I terminal.

There is a possibility that you did not fry the alternator when you had it hooked up with the bulb and ran it for a couple days successfully. When a part has a defect, it will usually blow out within the first few days or weeks of use, if it's going to go bad. It could be you just got a bad alternator and can get a warranty replacement.

[nikwho]

Originally Posted by dmjlambert

If you're going to have that kind of nature, open up that alternator and research the part number of the regulator and figure out how to verify if it's a PLIS or PLFS type. If you encounter a PLFS regulator in there, you can probably swap it for a PLIS regulator, and then you'd be all set and can proceed.

It's my nature to look for the safest way that works. I'm rather satisfied with the documentation that 67 Burb got from his friend, it looks like solid info there about the L terminal. When reading that information about the I terminal, that sounds OK also until you think about how that terminal position could be for F and we don't know how to wire that, and it certainly sounds like we shouldn't put 12V on it. The American Auto Wire article says the F pin is an output to provide field duty cycle information to the vehicles ECU. That same article says "Be forewarned!!!" about using the F/I terminal.

There is a possibility that you did not fry the alternator when you had it hooked up with the bulb and ran it for a couple days successfully. When a part has a defect, it will usually blow out within the first few days or weeks of use, if it's going to go bad. It could be you just got a bad alternator and can get a warranty replacement.

Here is my thought on that logic. You're thinking take it apart, see if is the correct regulator, and replace it if it isn't. I suppose that you could just hook it up. If its correct, it works. If it isn't correct, you were planning on changing the regulator out anyway... Doesn't matter if the old one that you're replacing is burnt up or not, right? I haven't read about any collateral damage when the voltage regulator burns up. So, why do the research?

I've already got the new pigtail on its way. Will be delivered Monday. I'm going to go that route, since it's known to be safe. But, it's tempting to try...

Good point about the possibility of not frying my last alternator!

[dmjlambert]

Yes, that is interesting. That would be a good approach. I don't always think that logically. I wonder if it's easy and somewhat cheap to buy those regulators. I wonder if you took the alternator into a car parts store to have it tested if they would tell you it needs a regulator. So did you hook up I, L, and S as shown in that Rebel diagram? If you only hooked up L and S, I wonder if it would come to life if you disconnected L and hooked up I.

[nikwho]

No sir, I did not wire it according to the Rebel supplied diagram. Ive been waiting for my ACDelco adapter pigtail, with resistor wired inline.

There are some interesting pieces for sale here:
https://store.alternatorparts.com/cs130-regulator.aspx

Looks like a few good options.

[67 Burb]

After checking-out that link Nikwho posted, there seems some of the regulators can use 12V to the "F/I" terminal and some can't.

Here is the charging circuit diagram for a 1988 GMC pickup. I shows only the dash light connection used. I looked at the diagrams I have for 1994 and 1995 Chevy trucks and they are basically the same as the '88 one To be safe, just install a dash light (or a resistor that will give you about 2.5V) and use the "L" terminal connection.

My alternator is a rebuilt one, so it may have a regulator different than the original.

[67 Burb]

Here's the indicator dash lights diagram. There is a resistor in the "volts" indicator circuit in case the bulb burns out, but it doesn't give a value. I think someone somewhere mentioned a resistor value that you could use instead of the light. As you don't need the light as you have the volt gauge.

[gmc684x4]

My parts truck donar is a 91 c1500 i also have a gm service book for the 91 its print shows brown wire to L terminal and a optional second wire

Truck has only L terminal wire to Cs130 alt and since L is always L
Makes me think that is why Aaw diagram is wire to L terminal to help eliminate reman alt with other style regulator installed from burnning out