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Thread: E36 LSX - alternator light

  1. #1
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    E36 LSX - alternator light

    Anyone figure out or try to connect make this work with the BMW dash light?

    The F-body has a charge/alternator gauge, when it gets below a certain range the "Check Gauges" light is illuminated.

  2. #2
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    Um, connect the wire for the BMW alternator light (X-20 pin 25 is as good a place as any) to any switched 12 volt source...
    Last edited by rao; 01-06-2010 at 05:36 PM.
    Rob
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  3. #3
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    Ok, yea but I'd light for the alt. light to come on when the alternator is crapping out or not putting out 12+ volts.


    The 1999' F-body GM PCM red conn. pin 15 (wire color red) is labeled "Generator Turn On Signal". Of course I only have schematics for the 98' F-body but it appears this wire is for the dash lamp signal. I was thinking it's not as simple as connecting this wire the BMW alternator light dash wire?

  4. #4
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    What I said will do that.

    What you are taking about is an entirely differnt thing - it is a unique 98 LS1 item that turns on the alternator.
    Rob
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  5. #5
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    Quote Originally Posted by rao View Post
    Um, connect the wire for the BMW alternator light (X-20 pin 25 is as good a place as any) to any switched 12 volt source...

    Do you know how the dash light is set up to illuminate whenever the voltage drops below a predetermined range?

    Essentially connecting it to any switched 12v source won't immediately let you now when the alt. has stopped charging. It will let you know once your battery has been pulled down below 12volts due to a dead alternator.

    Just want to understand exactly how this works and not blindly follow what someone else has done even though I'm sure you set up works fine.

  6. #6
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    No problem - ignore my posts

    Good luck.
    Rob
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  7. #7
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    Quote Originally Posted by rao View Post
    No problem - ignore my posts

    Good luck.

    LOL thanks.

    Just trying to understand why and how it works, not disagreeing with your method.

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    Connecting the bulb to just any switched 12V source defeats the purpose of the charge light and is not the correct way to do it. One end of the charge light is connected to 12V and the other end should be connected to the alternator "turn on terminal" (Terminal L)

    When you turn your key to the on position without running the engine, the current flows from the 12V source through the bulb and grounded at the alt. This illuninates the charge light.

    Once you start the engine, the alt is turned on and it sends 12V to the bulb. Since there is 12V on both terminals of the bulb, the charge light will no illuminate.

    In the event the alt fails, it will not send 12V but rather will ground the circuit and hence the charge light will come on.

    the 1998 F bodies are wired differently than the 99+ cars. In the 99+ cars, the PCM turn on the alt and when the alt fails, the PCM send a signal to the F-body cluster

    here is a very useful thread on the tech
    http://www.ls1tech.com/forums/conver...aq-thread.html

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  9. #9
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    Quote Originally Posted by Schitzo View Post
    Connecting the bulb to just any switched 12V source defeats the purpose of the charge light and is not the correct way to do it. One end of the charge light is connected to 12V and the other end should be connected to the alternator "turn on terminal" (Terminal L)

    When you turn your key to the on position without running the engine, the current flows from the 12V source through the bulb and grounded at the alt. This illuninates the charge light.

    Once you start the engine, the alt is turned on and it sends 12V to the bulb. Since there is 12V on both terminals of the bulb, the charge light will no illuminate.

    In the event the alt fails, it will not send 12V but rather will ground the circuit and hence the charge light will come on.

    the 1998 F bodies are wired differently than the 99+ cars. In the 99+ cars, the PCM turn on the alt and when the alt fails, the PCM send a signal to the F-body cluster

    here is a very useful thread on the tech
    http://www.ls1tech.com/forums/conver...aq-thread.html
    Great info.
    Now which wire from the 99' GM PCM should connect to the BMW alt. light?
    I don't see anything called out on the PCM pin out sheet that gives any indication. Maybe I missed it?

    The alternator has a red wire on the L terminal that runs back to pin 15 (red conn) on the PCM and that's the only place it goes.
    Last edited by Demon Speed; 01-06-2010 at 08:20 PM.

  10. #10
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    did you think of just getting a battery gauge?
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  11. #11
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    Quote Originally Posted by Demon Speed View Post

    The alternator has a red wire on the L terminal that runs back to pin 15 (red conn) on the PCM and that's the only place it goes.
    That Red wire is what the PCM uses to activate the alternator and also monitor the alt function.

    You have two options. Leave it as is (the red wire connected to the PCM) or connect that red wire from the alt the charge bulb (no connection to the PCM)

    2003 M5 LSx l 6 Spd Manual l 4.10 LSD
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  12. #12
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    Quote Originally Posted by Schitzo View Post
    That Red wire is what the PCM uses to activate the alternator and also monitor the alt function.

    You have two options. Leave it as is (the red wire connected to the PCM) or connect that red wire from the alt the charge bulb (no connection to the PCM)
    Would it be fine to just splice into the red wire connecting it to the charge bulb and leaving it connected to the PCM too?

    If I cut the wire away from the PCM then will it no longer activate the alternator? I'm not familiar with how the PCM activating the alternator works.

    Quote Originally Posted by Volcom8190 View Post
    did you think of just getting a battery gauge?

    I already have aftermarket oil temp and pressure gauges. I'd be happy if the Alt. light would just work. No need for additional gauges.
    Last edited by Demon Speed; 01-06-2010 at 09:40 PM. Reason: Automerged Doublepost

  13. #13
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    When the car cranks, the alternator needs power to "excite" it. The red wire from the PCM supplies this power in a GM car. Once the car starts and the alternator spins up and produces power, the voltage from the PCM is cut off.

    If you want the alternator light on the dash to work, abandon the PCM red wire, and route power to the alternator using the BMW circuit that is already in the car. Look at the ETM (BMW Electrical Troubleshooting Manual) page covering the Charge Circuit to figure it out. You will run a new wire from the plug that used to connect to the BMW alternator, and connect it to the terminal that the GM alternator uses.
    Last edited by garretvs; 01-07-2010 at 01:15 AM.



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  14. #14
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    Quote Originally Posted by garretvs View Post
    When the car cranks, the alternator needs power to "excite" it. The red wire from the PCM supplies this power in a GM car. Once the car starts and the alternator spins up and produces power, the voltage from the PCM is cut off.

    If you want the alternator light on the dash to work, abandon the PCM red wire, and route power to the alternator using the BMW circuit that is already in the car. Look at the ETM (BMW Electrical Troubleshooting Manual) page covering the Charge Circuit to figure it out. You will run a new wire from the plug that used to connect to the BMW alternator, and connect it to the terminal that the GM alternator uses.
    Thanks, that's the info I was looking for.

  15. #15
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    As luck would have it the exciter wire to my alternator snapped today

    My battery light came on immediately (I also have a volt meter so I knew the alternator was not working). I will have to check my notes and see just how I wired the light - at least I now know that it works
    Rob
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  16. #16
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    Yea, I need to get this working on my car before I'm left stranded.

    When I owned a 99' Trans Am the alternator crapped out on it at 40k miles and then again at 80k miles. Both were OEM (AC Delco) alternators. Possibly due to heat? I installed headers on it early on.

  17. #17
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    Following the description that Schitzo gave in post #8, if the alternator goes out while connecting the light as per Rao's (any switched 12+ volts) Shouldn't the light come one within a minute (as it did for Rao)?

    There is only one source of charge within car's circuit. As soon as you take away the charge the voltage drops right away as battery cannot sustain running car for more than few minutes.

    I think you can do it both ways, the only difference would be is your light comes on right away when Alt. fails or within a minute or so, which I don't thing makes a lot of difference at this point. Of course if you can connect it the proper way it would be better option.
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  18. #18
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    Quote Originally Posted by bimerok View Post
    Following the description that Schitzo gave in post #8, if the alternator goes out while connecting the light as per Rao's (any switched 12+ volts) Shouldn't the light come one within a minute (as it did for Rao)?

    There is only one source of charge within car's circuit. As soon as you take away the charge the voltage drops right away as battery cannot sustain running car for more than few minutes.

    I think you can do it both ways, the only difference would be is your light comes on right away when Alt. fails or within a minute or so, which I don't thing makes a lot of difference at this point. Of course if you can connect it the proper way it would be better option.
    Not entirely true. A good battery will keep a car running for a quite a while with a dead or non charging alternator. I did it each time mine died.

    The second time I had a new Optima battery and drove around for a whole day (a few hours) with a bad alternator.

    Hence my reasoning for wanting to connect the charge lamp the correct way, which should indicate when alternator is not charging not when the battery is below 12 volts.
    Last edited by Demon Speed; 01-15-2010 at 02:56 PM.

  19. #19
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    Conventional alt light works like this:

    12v direct from battery to ignition switch to charge light on dash
    Current from light to wire on alternator
    Alternator provides ground for light circuit when not turning (engine not running)
    Alternator spins up, 12v from light excites it; it starts to charge
    Ground for light no longer effective when alternator spinning and producing "enough" voltage: 12v is being fed back to the light -- the light now goes out since it has 12v on both of its wires.

    See:

    http://www.familycar.com/Classroom/charging.htm



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  20. #20
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    While finishing up the LSx M3 wiring, got to the charge light and being gun shy from horror stories in the past of short lived late model GM alternators due to improper wiring, did a bit of searching and found many sources confirming garretvs advice.

    For the E36, the charge light is powered +12v from the key in run and start position, so just take pin 25 from the X20 connector, (BLUE wire), and connect it directly to the “B” terminal of your F-body/Truck alternator and that’s it.


    John from Speartech advice;

    Quote Originally Posted by Speartech View Post
    …. the single wire to the alternator should not be a direct 12 volt line. This is the "lamp" terminal of the regulator and is designed to have a voltage drop across it for proper operation and long life. It was originally designed to have an idiot light between it and 12 volts.
    It is NOT the "field" line, as this is internally connected on the F-body alternator.

    If you don't want to add a light to your setup (most people don't), you should go to radio shack and buy a 500 ohm resistor and put it in series with that line.

    The correct sequence is: Ignition switch 12 volts to one side of resistor; (or bulb), other side of resistor, (or builb) to terminal B of the regulator.

    Your alternator will thank you in a couple of years, as it will still be working! <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />
    Quote Originally Posted by Speartech View Post
    It just like the sequence I described above, only you use a bulb instead of a resistor. The regulator in the alternator will ground the line when the alternator is off, which causes the light to be on. Then when the alternator turns on, the line is no longer ground (by design) so the bulb goes off.
    With it wired up this way, if certain failures take place inside the alternator, the light will come on alerting you to a problem.

    John

    Another great post with diagrams;
    Quote Originally Posted by G-Body View Post
    All of the alternators used on LSx engines have 2 connection points.
    1. The main output stud on the back. Connect this to the + battery cable/terminal or to the main power distribution center.

    2. The 4 pin weatherpack connector. There are 4 pins, but not all 4 are used in every application. See posts below to determine which one(s) are needed.

    If you are hooking up the alternator using the wiring harness and PCM from the same bodystyle vehicle as the alternator the wiring is already done, unless you have a 1998 f-body PCM/harness.

    If you are not using the factory harness/pcm or are using a 1998 f-body harness PCM refer to diagrams below.

    1998 F-body

    1999-2002 F-body

    Corvette

    Trucks 1999-2000

    Trucks 2001-?

    Somewhere around 2003 the trucks or at least some of them started using 3 of the 4 wires, but I don`t know if it all of the trucks started this at the same time or if only some models are using 3 wires. If anyone has any wiring diagrams for the 2003 and newer and could post them or send them to me that would be great. I don`t have any info for the GTO`s or the FWD (new monte/impala) yet either.

    Heres a link to the resistors http://www.radioshack.com/product/in...tId=2062320&cp

    Heres a link to the original alternator thread http://www.ls1tech.com/forums/showthread.php?t=40815


    Hope that helps.

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  21. #21
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    I just found this thread when searching about hooking up my GTO alternator in place of my F-body alternator.

    I was told that the GTO alternator is self exciting and mine is stamped with 140A. Hopefully this will be enough to power my stereo and all my other electronic gadgets.

    Thanks to everyone who posted in here for explaining it in extremely simple terms.

  22. #22
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    Great info.
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