Charging problem I can't figure out.

[Ishmael]

I've tested all kinds of stuff on this and been on google and youtube. I can't figure it out. I have an aluminum LS2 out of a C6 vette in my 68 firebird. I can't get my alternator to charge. My battery is good and the alternator is a reman. I get 11.7 off both when the engine is running. There was a blown fusible link to the voltage regulator. I have 11.7 coming off the orange wire and off the brown. If I jump from the orange directly to the blue I get nothing but a spark and it didn't get the alternator going but I don't think it would because the blue wire coming off I think goes through the factory engine harness to the alternator and is no longer used. Besides isn't the LS2 alternator (4 wire) internally regulated? If I'm right either the reman alternator has a faulty regulator or the computer isn't programmed properly to start the alternator or the external regulator is supposed to somehow to something and that blue wire is supposed to somehow get connected to the alternator. Either way I got no change in voltage after jumping the orange to the blue at the regulator. What are your thoughts?
TIA

[dhutton]

You still have the original external regulator connected? It needs to be removed and bypassed.

Don

[Ishmael]

Well that's good to know. How do I bypass?

[dhutton]

Sorry I always do a complete rewire so I don’t know the details. For a start just unplug it. Did your LS harness come with the plug for your new alternator?

Don

[Ishmael]

Sorry I always do a complete rewire so I don’t know the details. For a start just unplug it. Did your LS harness come with the plug for your new alternator?

Don

It did. So with it unplugged the car still runs - just doesn't charge. So I don't need the stock external regulator? Is there a way to test the wiring to the alternator or the regulator in it? I get 11.5v off the battery post on the alternator and the battery.

[dhutton]

Good wiring diagram here:

https://www.camaros.net/forums/attachment.php?attachmentid=149809&d=1464084803

[dhutton]

Did your LS harness include the alternator plug? Most auto parts stores can test the alternator for you.

You don’t need the stock external regulator with an LS internally regulated alternator.

Don

[Ishmael]

Thanks Don. And thanks for the schematic. I've seen some but that was one of the clearest. The harness included the plug. I will get the alternator tested. I suspect either there is something missing from the harness (I keep reading about a resistor or a diode or something), or the computer isn't sending the message to excite the alternator.

[dhutton]

Make sure the engine, frame, and body are properly grounded.

[Ishmael]

Make sure the engine, frame, and body are properly grounded.

I’m pretty sure it’s all grounded.

[blitzer454]

Thanks Don. And thanks for the schematic. I've seen some but that was one of the clearest. The harness included the plug. I will get the alternator tested. I suspect either there is something missing from the harness (I keep reading about a resistor or a diode or something), or the computer isn't sending the message to excite the alternator.

If it is a 4-wire alternator then you will need to connect the "I" terminal of the alternator to a switched 12V source via a resistor in order to excite the alternator before it starts to turn otherwise it won't charge. This may be the resistor you heard about?? The "S" terminal of the alternator should be connected to the main junction point of the car which for a 68 firebird would be the horn relay.

[dhutton]

If it is a 4-wire alternator then you will need to connect the "I" terminal of the alternator to a switched 12V source via a resistor in order to excite the alternator before it starts to turn otherwise it won't charge. This may be the resistor you heard about?? The "S" terminal of the alternator should be connected to the main junction point of the car which for a 68 firebird would be the horn relay.

That connection is normally supplied in the LS conversion harness alternator plug. At least it has been in all the ones I used.

Don

[blitzer454]

That connection is normally supplied in the LS conversion harness alternator plug. At least it has been in all the ones I used.

Don

My harness had a wire labeled GEN but it was never clear to me if that was meant to be used as the exciter wire or if that was a PWM wire to be used on the newer alternators that support that feature. Originally I was using it as the exciter wire and it was working, but in the end I decided to use a resistor to a switched supply.

[dhutton]

My harness had a wire labeled GEN but it was never clear to me if that was meant to be used as the exciter wire or if that was a PWM wire to be used on the newer alternators that support that feature. Originally I was using it as the exciter wire and it was working, but in the end I decided to use a resistor to a switched supply.

There is a long thread about this somewhere on here. It was determined that the harness provides the correct resistor connected to a switched supply. At least that is my recollection.

Don

[Ishmael]

So I took it into the parts store to get the battery and alternator tested and when the guy at the store hooked up his machine it was reading 14.1v when the fan, stereo and lights were on it was 13.8 or thereabouts. My multimeter tested the same. When I got it home it was back to 11.6v.
I would assume the alternator then isn't the culprit. The battery checks out. The computer must be good because it sent the signal to start the alternator and the harness must have whatever it needs in it. Can a horn relay cause this and can they go good and bad? Unless a diode or whatever is being used for resistance can go in and out it has to be a connection, a ground or a broken wire in the harness and since I have already had one of those, things could get interesting. I have an aluminum engine block. I have heard about issues there but I have ground straps from the engine to the body and the frame and cables off the battery to the frame and the block.
My wife won't go anywhere in the car and I don't blame her.
What am I missing?

[dhutton]

Did you put a voltmeter right on the alternator post and measure the voltage with the meter ground on the block? What does it read?

Are your fans running when you are doing this test?

Don

[dhutton]

Who made your harness?

[Ishmael]

PSI made the harness but it was years ago. I have had problems with either the harness, the connection to the trans or the tune that has stopped me from driving it forever. When I ground on the block I don't get any change.

[Ishmael]

Sorry it goes from 11.6 Just off the battery to 11.4 off the post to the block.

[dhutton]

What is the voltage right on the alternator stud?

Don

[Ishmael]

As of right now everything off the stud on the alternator is 11.42. Across the battery though it’s 11.52 if that makes a difference.

[dhutton]

I would try the Holley alternator connector pigtail with the built in resistor as suggested by Blitzer.

Sorry, no other ideas. Hopefully Blitzer will weigh in.

https://www.holley.com/products/accessories/drive_brackets/components_and_service_parts/parts/197-400

Don

[Ishmael]

164347I will give it a shot. Do you know where the other end of that wire goes? The pic is what I have going now. Since that red wire is turned around from the plug to the stud I don’t know where it was supposed to go just that psi told me to do it.

[130fe]

You can use one of these kits if you don’t want to cut your harness up (only use one of the pieces to bypass your old regulator.

https://www.classicmuscle.com/alternator-conversion-harness-for-internal-regulator-alternator-conversion-for-use-on-71-85-internal-regulated-alternators?utm_source=google_shopping&m=Abstract&gclid=EAIaIQobChMI_IGWipqh4gIVjMJkCh1LngnzEAQYCyAB EgLdbPD_BwE

Be sure to upgrade your charging wire (big wire) coming off of the alternator, the old size is too small for the new alternator. I would use at least 8awg or even a 4. I had a similar problem with my old C5 style alternator. I could only get 12.3v (under full load). Swapped in a larger charging wire and it helped a lot. Ended up switching to the new Holley Mid Mount SERP setup and now have 14.0v all day with everything running.

[Ishmael]

Thanks Chris. I will try upgrading that wire while I swap out horn relay. I might even try a second while alternator while I’m at it. If nothing else work I will order that adapter but I can get the Holley one at my parts store. I’ve emailed psi to see if that red wire was supposed to go elsewhere and if there was a resistor built in the harness and where. I’m going to order that plug Blitzer talked about.

[dhutton]

Information on that alternator here:

https://ls1tech.com/forums/conversions-hybrids/1875107-c6-corvette-alternator-wiring.html

Don

[Ishmael]

I searched 4 wire and didn’t come up with that. Should have searched c6 but who would have thought it would be different. I wonder if then there is enough resistance. I have an idiot light that does light up but the. Turns off once the engine starts. I will check what wire it is on. Would a 4 pin or 4 wire alternator from a truck be any different do you think? Psi doesn’t say anything about the alternator in their paper work. I bought the harness years ago from them. I can ask if there harness is set up for a c6 alternator.

[dhutton]

Reading through that thread I would try the Holley pigtail with the single wire. The other end is connected to switched 12 volts, the pink wire.

Don

[blitzer454]

The red wire that loops back is probably connected to the S terminal on the alternator. Connecting the S terminal that way will also work but it kind of defeats the purpose of the S terminal which is to sense the voltage at the end of the wire and have the alternator maintain the charging voltage at that point. It's better to maintain the charging voltage at the main distribution point not at the alternator.

If you have an alternator idiot light then the wire that goes to the exciter terminal on the alternator (which is the I or L terminal) is the wire that goes to this light. The light is on when you first turn on the key but will go out when the alternator starts to turn and generates its own voltage. The fact that your light is going off is a good sign and probably means that the exciter terminal is already connected properly.

Check the back of the alternator and see if the 4-pin connector has the letters printed on the alternator next to each terminal, I know mine did.

So it kind of sounds like your alternator is wired correctly and it actually works for a while but then fails. So it could still be a bad alternator or your drawing more power than the alternator can handle and it's going into thermal shutdown. This could happen if there was a partial short somewhere in the electrical system. You might try turning the key on engine off and measuring the current draw from the battery to confirm there is no short. Also check that the alternator is properly grounded to the battery ground. I think it probably is since you were measuring 11.42V at the alternator stud, unless you were using the alternator as your ground point when you took the measurement.

[Ishmael]

I contacted psi and they said the harness was sent out as a 2 wire plug. They knew it was a c6 so I don’t know what happened there. Somebody must have walked me through turning it into a 4 pin so I don’t know why we didn’t fix it then. They said the Holley plug wouldn’t work but I don’t know why. So my options are an alternator that has just a post and no wires, find an alternator that is two wires and would fit and change the plug or change the tune.

[Ishmael]

Hey Don and Blitzer thanks for all the help.

[dhutton]

Hey Don and Blitzer thanks for all the help.

Sorry I couldn’t be more help. Hope you get it sorted soon.

Don

[Ishmael]

Sorry I couldn’t be more help. Hope you get it sorted soon.

Don

You helped me through everything possible. I’m almost ready to get a new harness and tune. I am making plans to get it to the tuner.