Alternator 4 plug wire upgrade legacy 1992 with jdm ecu G2

[george 2022]

Hi. I want to upgrade the early legacy 1992 alternator with a newer 3 or 2 plug one.my alternator has the round plug with 4 wires Hitachi. I think the 4th one which is green with black stripe (D)goes to the ECU ???for some kind of Ecu control..I am not sure .does this wire leads to the Ecu ???I can not find a wiring diagram for this JDM ECU G2 226611AA950. The most early legacys 1990-4 came with 3 wires round alternator plug.!!!That's why I aske if it is possible to make the upgrade ?.

[mike-tracy]

Good Morning George. The American 90-94 Legacys came with a round plug like yours. There are wiring differences between the JDM, EDM, AUDM, USDM etc Legacys, though I'm not sure this is one of them.


The second post in this thread has links to the 90-94 Alternator and a newer alternator.
http://www.bbs.legacycentral.org/viewto ... 19&t=49364

If you have a different alternator than the example above, you need to connect at the minimum the "S" and "L" wires. Those are Sense and Light.


This is a view of the connector on the legacy alternator, not the plug side, so realize that the plug wires would be a mirror/reverse of this.


Another thread about adapting a Tribeca alternator, where I stole my information from:
http://bbs.legacycentral.org/viewtopic.php?f=19&t=52474

[george 2022]

Good Morning George. The American 90-94 Legacys came with a round plug like yours. There are wiring differences between the JDM, EDM, AUDM, USDM etc Legacys, though I'm not sure this is one of them.


The second post in this thread has links to the 90-94 Alternator and a newer alternator.
http://www.bbs.legacycentral.org/viewto ... 19&t=49364

If you have a different alternator than the example above, you need to connect at the minimum the "S" and "L" wires. Those are Sense and Light.


This is a view of the connector on the legacy alternator, not the plug side, so you don't get them reversed.
My alt is that with the round plug (D) wire.it's JDM. So is it safe to cut this wire for the newer alternator upgrade? Where does this wire go?

Another thread about adapting a Tribeca alternator, where I stole my information from:
http://bbs.legacycentral.org/viewtopic.php?f=19&t=52474

[mike-tracy]

George, you can tape up that wire and tuck it away. I don't know if you caught my edit, but remember that the wiring on the plug side is reversed compared to the diagram above.

I believe the D wire connects to the ECU, which sends it a signal to turn on. The newer alternators turn on automatically with an internal RPM sensor.

[george 2022]

George, you can tape up that wire and tuck it away. I don't know if you caught my edit, but remember that the wiring on the plug side is reversed compared to the diagram above.

I believe the D wire connects to the ECU, which sends it a signal to turn on. The newer alternators turn on automatically with an internal RPM sensor.

That's true this D wire connects to the D21 pin out of the ECU. That's what I wanted to hear that it safe to tape it up and tuck it away.the last thing is that i dont want is to destroy and burn the ecu.!!which newer alternator do you suggest for the upgrade? The 3 or the 2 plug wire? Thanks for the replies.

[mike-tracy]

The 2 or 3 wire newer models don't make a difference. Something from a mid 2000s Subaru should be in the 90 amp range, though you might need to check online to confirm. Let us know how this works out.

[george 2022]

George, you can tape up that wire and tuck it away. I don't know if you caught my edit, but remember that the wiring on the plug side is reversed compared to the diagram above.

I believe the D wire connects to the ECU, which sends it a signal to turn on. The newer alternators turn on automatically with an internal RPM sensor.

That's true this D wire connects to the D21 pin out of the ECU. That's what I wanted to hear that it safe to tape it up and tuck it away.the last thing is that i dont want is to destroy and burn the ecu.!!which newer alternator do you suggest for the upgrade? The 3 or the 2 plug wire? Thanks for the replies.

The yellow one IG wire turn on the alternator.I understand this.for what reason needs the alternator also the D green wire .2 wires to turn on the alternator for charging.we miss something here....

[mike-tracy]

People on this board have been successfully running 2 wire alternators by only connecting the S and L wires to the new plug. Are you saying yours isn't working, or are you concerned about the IG and D pins not being used?

[george 2022]

People on this board have been successfully running 2 wire alternators by only connecting the S and L wires to the new plug. Are you saying yours isn't working, or are you concerned about the IG and D pins not being used?

I am concerned about the D pin.one last question.the D pin recieve signal from Ecu or send .?

[mike-tracy]

I'll look through the service manual after work and get back to you.

[george 2022]

I'll look through the service manual after work and get back to you.

Thanks and sorry if I was annoying.if can send me the wiring diagram for this JDM ECU G2 I would be very happy. I do have many diagrams and service manuals but nowhere shows that that D pin from alternator goes to the D21 Ecu.all of the diagrams that I have shows that D21 or F47 .21 are empty.

[mike-tracy]

I don't have the service manual for the (unspecified country) Legacy you have. I have the 1991 USDM Legacy FSMs. I am running a japanese ej20g ecu in my USDM Legacy, the only wiring change i made was an ignition converter to allow the ecu to run wasted spark.

You have mentioned the G2 ecu a couple times now, what is that from originally?

[george 2022]

I don't have the service manual for the (unspecified country) Legacy you have. I have the 1991 USDM Legacy FSMs. I am running a japanese ej20g ecu in my USDM Legacy, the only wiring change i made was an ignition converter to allow the ecu to run wasted spark.

You have mentioned the G2 ecu a couple times now, what is that from originally?

I bought that in Germany and it is japan import JDM.I have speeded hundred of hours in the net ,I came in contact with subaru Germany I spoked with small cars , mountain westy about this Ecu and wiring diagram without success. Only with subaru in Japan I haven't come in contact and the reason is my knowledge in japanisch. Totally frustrated.

[mike-tracy]

This is what i have in my car. My Japanese ej20g ecu runs the alternator without the pin connected to anything. No codes, or any other funny actions. I'll double check when i get home, but i can tell you right now my service manual won't have anything . Most likely the alternator is a generic one with a 4th wire going to a function that exists on a different car. This is supported by you not finding anything in your literature and scans.

[mike-tracy]

The 1991 and 1992 USDM service manual has different plug and pin numbers than your information. It is called plug f10, and every description lists only pins f10.2, f10.3, and f10.4. Pin 2=S, pin 3=L and pin 4= IG. There is no reference to pin 1 ("D" in the diagram I posted earlier).

I did find an Austrailian 1992 "Liberty" service manual, these are a lot closer to your car electrically, with the water-air intercooler, ej20g engine and coil on plug ignition.
http://bbs.legacycentral.org/viewtopic.php?t=14485
section 6 has the electrical:
http://www.main.experiencetherave.com/s ... SM_-_FULL/

[mike-tracy]

Under section 6 of the Australian service manual, the alternator plug is F17. Only 3 pins are listed. F17.2, F17.3, and F17.4, and those pins have the same functions as the US model. This starts on page 178 in the Section 6 zip file.

It is my belief that you will be fine just connecting the S and L wires to the new alternator.

[george 2022]

The 1991 and 1992 USDM service manual has different plug and pin numbers than your information. It is called plug f10, and every description lists only pins f10.2, f10.3, and f10.4. Pin 2=S, pin 3=L and pin 4= IG. There is no reference to pin 1 ("D" in the diagram I posted earlier).

I did find an Austrailian 1992 "Liberty" service manual, these are a lot closer to your car electrically, with the water-air intercooler, ej20g engine and coil on plug ignition.
http://bbs.legacycentral.org/viewtopic.php?t=14485
section 6 has the electrical:

Thanks for the try to solve my problem.as I said I do have almost all the 1990-1994 service manuals and usdm or ausdm and others
In all of them the D .21 pinout on the Ecu is empty.at my Ecu the D.21 pinout from Ecu connects to the D (dummy) wire (green with black stripe)pin of my round 4 wires
Plug alternator. Also the yellow wire Ignition
is connected as it must .through ignition relay and ecu ...I know all of them and I have studied the wiring diagrams very carefully. My question is WHY from my ecu plug with the 26 pins also labelled according the the diagrams D. So from D.21 runs a cable to the 4th.wire of my alternator.????
So I have 2 wires the yellow one from the alternator which goes through fuel relay to ignition relay to switch ignition on and all of them toEcu B.12 pin out plug and the 4th wire from the alternator which goes to the ECU D.21 pin out .that's why I am concerned about the upgrade...
http://www.main.experiencetherave.com/s ... SM_-_FULL/

Just searching in the net how an alternator works .....maybe that S terminal is our D terminal in the alternator plug and that's why it's connected to the ECU and I imagine the ecu regulates the amount of voltage and says the alternator how much to charge.... what is your opinion?????

STOLEN FROM AN ALTERNATOR SITE

S terminal - Senses battery voltage so that the alternator knows how much effort to put in. It should be wired to a power source.
IG terminal - This is the terminal that turns the voltage regulator on. It is wired to the power source from the ignition switch.
L terminal - Closes the circuit to the charging system warning lamp. If the alternator stops doing its job, this terminal becomes the ground for the warning lamp, which turns the lamp on. When working properly, this terminal will show battery voltage.
B terminal - Alternator output terminal. This should be connected to the battery, as it is where all the electricity comes from.
F terminal - Full-field bypass for regulator. This is for testing purposes only. It's best not to mess with it.

[mike-tracy]

Hi George, I think it is only a problem if your alternator is doing something its not supposed to do. What you said about that pin being a diagnostic pin from the manufacturer makes sense. I don't think they would support a 25 year old product, but did you contact the alternator manufacturer directly?

[george 2022]

Hi George, I think it is only a problem if your alternator is doing something its not supposed to do. What you said about that pin being a diagnostic pin from the manufacturer makes sense. I don't think they would support a 25 year old product, but did you contact the alternator manufacturer directly?

Talk directly with Hitachi? Where in Japan?I will try thanks anyway.