E32 battery charging issue

[JMCLuimni]

I recently bought a low mileage e32 740iL. Car had history, one previous owner, of not charging battery before it was put in storage 12 years ago.

Symptom:
1. Battery won't charge. Battery is brand new
2. Battery symbol in dash does not light up. Battery bulb in dash tested fine
3. Battery will take and hold a charge from external charger
4. Is there an easy way to check the alternator output without putting the car up on jacks and removing the lower engine cowel?

Can anyone tell me why that battery light may not be lighting up?
From reading articles on the light , I understand that the light not working can cause the battery not to charge. If this is the case, then replacing the alternator with the dash light issue not resolved will be a waste of time and money. It seems like removing the alternator is a PITA and something I'm not interested in tackling. I want to avoid bringing the car to an independent if the problem is a simple one like a fuse or bad earth/ground wire that someone on this forum may have experience with.
What relation does the dash battery light have with the alternator? It seems from circuit diagrams that the light is powered when the ignition key is turned and gets its power from the battery itself.
Is there a simple way to test the alternator output without putting the car on jacks and removing the lower tray?
Any help appreciated....

[bmwdirtracer]

We need Shogun here. I am damned good at electrics, but I can't even begin to fathom the unloader relay function in this car's diagrams:

http://wedophones.com/Manuals/BMW/19...g%20Manual.pdf

See page 115 of the Adobe document.

I'd have to say that you need to check and/or replace fuse numbers 17 and 28, and get yourself a new Unloader Relay K61, from the dealership.

Better yet, do whatever Shogun tells you to do; he's the MASTER of this car. I'll ask him to visit your thread.

[shogun]

I am not an electric expert, but on the older cars the alternator needs the bulb as exciter light, So either the bulb is the problem or the wire from alternator to the cluster, usually from my experience the connector left side next to the B+ post.
here is a copy of a good write up below. There is a cable going from the alternator to the connector next to the B+pole in engine bay, 2 of them are for the engine oil level, and one is the exciter cable from the alternator to the cluster.
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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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Now back to the E32, 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

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

[shogun]

Some additional info today received from E32Fan:
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