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Thread: 1990 E32 735i Alternator Fuse and Relay location

  1. #1
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    1990 E32 735i Alternator Fuse and Relay location

    Anyone know where the Atlernator Fuse and Relay located on a E32 735i 1990? My battery is fine but my alternator is not charging at all. Before I replace it, I want to check if the alternator is really bad?

    Just need the location of fuse and relay for alternator. Thank you

    Happy Holidays!
    Last edited by shogun; 11-03-2015 at 06:00 AM.

  2. #2
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    Before diagnosing alternator problems there is one thing to mention. Alternators use an "exciter" voltage to get the alternator working when you start your car. About 90% of the cars made today run that 12 volts through the "battery" or "alternator" bulb (AKA the idiot light). you need to check to see if this bulb is not burned out. It should light when the key is turned on! If it doesn't then there is a very good chance that the alternator will not put out! Replace the bulb before beginning the rest of the diagnosis."


    http://forums.bimmerforums.com/forum...ht=idiot+light





    fuses, relays and wiring diagrams are here
    http://shark.armchair.mb.ca/~dave/BMW/e32/
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  3. #3
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    Alternator Bulb Aka "Idiot Bulb" Location

    Hey Showgun,

    I attached the diagram of the cluster where the "Idiot Bulb" for the alternator is located. Is that bulb special or is it like any other standard bulb suck as the other ones on the cluster.

    * Can this alternator bulb be a special bulb becuase of its unique fuse capabilaty?

    Thanks

    Joe
    Attached Images Attached Images

  4. #4
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    I assume it is a normal bulb, but I am not the electric expert
    Shogun tricks and tips for the E32 series are HERE!

  5. #5
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    It is a regular 1.2 watt Black Base bulb.

    The Brown Base bulbs that are used for the digital display backlight are 1.5 watts.

  6. #6
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    Idiot bulb

    My battery is not charging and this battery symbol light does not come on in the dash. Am I to assume that the battery will not charge if this bulb is blown?
    thanks
    Quote Originally Posted by E32FAN View Post
    It is a regular 1.2 watt Black Base bulb.

    The Brown Base bulbs that are used for the digital display backlight are 1.5 watts.

  7. #7
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    Now we all know why it is called an IDIOT LIGHT!
    One of my neighbors came over to seek my advice on a baffling problem he was having with his GM and its charging system. He was having dead battery problems and had taken his alternator off to replace it. Fortunately he had taken it to "Wheels" the former National Auto store, and they had tested it on an alternator testing machine. There was nothing wrong with it. This neighbor, I'll call him Artie, had the foresight to do some diagnostics ahead of time and determined that there was no output (14.5 volts) at battery or at the alternator stud, so a logical conclusion was that the problem was in the alternator - it has a built in voltage regulator so logic prevailed. Replace the alternator and solve the dead battery problem, right? Nope.

    We had the service manual open to the circuit describing the charging system. I traced the wires and determined which one was the field and which was the bat and which one was ground. Then I noticed something strange. I thought it was a typo - the wire from the 12 volt source to the field winding went through the idiot light filament, that's right, the bulb is in series with the field supply. Alternators don't have a true field supply like the old generators had with external voltage regulators which regulated the output by switching the field winding on and off. But they do need something to start the system working. Once the system is putting out its current the system becomes sort of self sustaining.

    I took a short length of wire and connected it to the field terminal while the engine was running. Suddenly, the voltmeter across the battery went to 14.5 volts! I took the wire off the terminal and sure enough the system continued to charge at 14.5 volts. Fixed, right?? Nope.

    Artie shut the engine down and restarted it again - nothing - jump the field, 14.5 volts.

    I asked Artie if the idiot light was on while it was running and not putting anything out. Nope. He shut it down again and we tried it all over again, only this time I sat in the driver's seat and Artie did the jumper thing. Same results, only I did notice something strange. "Just where is the "alt" idiot light on the dash panel Artie? I didn't see one - just an engine light and an oil pressure light."

    There was no idiot light for the charging system! I took a flashlight and held it at an angle to the dash panel. There, not visible under normal lighting conditions, was a place for the "bat" light. Yet it did NOT light when the switch was turned to the "ON" position. Then it hit me like a ton of poop! Remember I thought that the circuit diagram was in error - that the idiot light was shown to be in series with the field terminal on the alternator?? Well, that was not a typo! The bulb in the dash panel is part of the charging circuit. It is REQUIRED to be functional to supply the initial field voltage to get the alternator started doing its thing. IF THE BULB IS BURNED OUT THE SYSTEM WILL NOT CHARGE!!

    It took us another half an hour to get to where the bulb should be but it became obvious that it was going to take a LOT more than a half hour to replace the bulb. It looked like part of the instrument cluster was going to come out before we got to the bulb. Plan "B" went into effect. I found the wire under the hood that supplies the idiot light and wired in a small socket and a bulb under the hood. I connected the other end of the wire to the field terminal and started it up. Voila! Charged just like new. I taped the bulb and socket to a handy vacuum hose and closed the hood. To this day that GM product is still riding around with a bulb taped to the vacuum line under the hood. I would love to see the face on the mechanic who discovers that bulb and wonders what the heck it is doing there!!
    From Howstuffworks
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  8. #8
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    Hi Shogun
    Great write up. I pulled the steering wheel and instrument cluster out. Checked the Battery light bulb and it works fine. Battery is not charging. I've checked volts everywhere except at the alternator itself and no charge.
    Why would the bulb not light up?
    Is checking the charge in engine bay of an e32 the same as gettting under the car and checking it directly from alternator directly?
    My electrical knowledge is basic at best....
    Thanks
    Last edited by JMCLuimni; 03-19-2017 at 07:55 PM.

  9. #9
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    Most probably the exciter cable.
    the plug is shown here http://bmwe32.masscom.net/sean750/sp...ewLeftBank.jpg
    colors of the plug wires blue-pink-brown, see on my website under fixes >>>>Electrical power>>>Replace charging cable between alternator and distribution post. http://twrite.org/shogunnew/topmenu.html

    Now to the backsite plugs of the cluster http://www.e32-schrauber.de/bmw/s-stecker-kombi.htm
    X16 yellow plug pin 5 blue cable A = out (E = in) Ziel = going to>>LIMA = alternator, Beschreibung = description, Ladekontrolle = charging control http://www.e32-schrauber.de/bmw/date...ung-x16-93.pdf

    Often the plug next to the B+ pole is the problem, BMW does not sell it, but on my website in that link above it shows the equivalent to the Bosch plug which fits.
    If an alternator is not charging the battery and the alternator light is on, the problem is likely to be the alternator, but if the alternator light does not come on at all when you turn the key, there is a problem with the light itself that has to be resolved first.
    https://www.bmwcca.org/roundel/troub...-warning-light

    My electrical knowledge is basic at best....
    then we are on same level ;-)

    Our E32 electronic expert E32Fan comments on this too
    "the Alternator requires some Current flowing in its Field winding before it can generate any power (even with the engine running). The source of this current is through the charge indicator light, into the BLU wire feeding D+. (BTW - The resistor shown in parallel with the lamp will provide some Field current even if the lamp burns out.) When the alternator starts generating its own voltage, then the 3 diodes feeding D+ will raise the D+ pin to 12V, so the charge light goes out. "

    https://www.bimmerforums.com/forum/s...rnator+exciter
    https://www.bimmerforums.com/forum/s...rnator+exciter
    Last edited by shogun; 03-20-2017 at 12:21 AM.
    Shogun tricks and tips for the E32 series are HERE!

  10. #10
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    Quote Originally Posted by shogun View Post

    Our E32 electronic expert E32Fan comments on this too
    "the Alternator requires some Current flowing in its Field winding before it can generate any power (even with the engine running). The source of this current is through the charge indicator light, into the BLU wire feeding D+. (BTW - The resistor shown in parallel with the lamp will provide some Field current even if the lamp burns out.) When the alternator starts generating its own voltage, then the 3 diodes feeding D+ will raise the D+ pin to 12V, so the charge light goes out. "

    https://www.bimmerforums.com/forum/s...rnator+exciter
    https://www.bimmerforums.com/forum/s...rnator+exciter
    If the Alternator's field terminal goes open, then no current can flow through the idiot light lamp. The wiring diagram (Page 1230-00, -01) shows a resistor in parallel with the lamp at X16 pins 7 and 5, meaning that an open filament will not stop the field current. BMW engineers were not content to allow a blown idiot light filament to stop Alternator startup. This is a feature missing on 1990 GM cars, possibly.

    So I would suspect an Alternator fault. You can test this by sourcing some current via a 12V lamp into D100 Data Link Connector X6002 terminal 12. The pinout is shown at Page 8500-15

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