Battery light on when car is off?

[robbieosterman]

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[arnoldgtr]

It loks like you have a bad diode in the alternator. Remove the alternator and have it tested. They do it for free at places like Auto Zone, Advance, Pep Boys, etc.

[robbieosterman]

So, if it's a bad diode, do I have to replace the entire alternator?

[arnoldgtr]

There's a real mechanic talking!
Most people would throw on a rebuilt alternator...never mind that it's usually the $7 brushes that are worn out, or the little blue wire that fell off.
If you have a Bosch alternator, the ETK shows the diode pack, part #12-31-1-715-167. I would say it's a dealer only item.
You'll have to disassemble the alternator to replace the diode pack.
As long as you are in there, you might as well replace the brushes.
The brushes are available from BMW, too. The wire leads must be soldered in place, but all it takes is a soldering iron of about 45 watts.
Brush set, part #12-31-1-727-756.
HTH,

[robbieosterman]

Nice, now are those alternator part numbers meant for the M42?

[arnoldgtr]

Brushes are the same on all Bosch alternators.
Diode packs are different.
ETK shows 2 Bosch alternators installed on E30 M42.
For 80A Bosch alternator #0-120-469-919, use diode pack #12-31-1-727-749
For 90A Bosch alternator #0-120-469-914, use diode pack #12-31-1-727-750
HTH,

[chrisd]

this should be a sticky called "tech threads that don't suck and aren't flame wars"

[craig4ie]

H E L P

How was this fixed?? Was it a bad diode? Did you need a new alternator altogether?

Were the connections around the alternator/starter bad? Was it a voltage regulator?

My symptoms: Starts fine, runs fine...does everything fine.

Battery light is ON when car is OFF (key removed)...Battery Light is OFF when car is ON??? wtf?

[robbieosterman]

Old thread revival :)

I ended up throwing on a used alternator from another 318i and all of my problems disappeared.

H E L P

How was this fixed?? Was it a bad diode? Did you need a new alternator altogether?

Were the connections around the alternator/starter bad? Was it a voltage regulator?

My symptoms: Starts fine, runs fine...does everything fine.

Battery light is ON when car is OFF (key removed)...Battery Light is OFF when car is ON??? wtf?

[craig4ie]

Old thread revival :)

I ended up throwing on a used alternator from another 318i and all of my problems disappeared.

Haha yeah, I figured I would jumpstart this thread instead of starting a new one...search button FTW.

and...thanks for the prompt response man!! I've disconnected the battery so the draw from the light won't kill it. Once my exams are over I'll test another alternator and hope for the best.

[xLibelle]

robbie, wow, you found your thread from 3 years ago on the first day of revival!

[craig4ie]

Thanks to rkettner for quickly hooking me up with an alternator!

At first I swapped the voltage regulator from the new (used) alt to see if that was the problem, but it wasn't so I put the new (used) alt in and BAM! Problem solved!!

Thanks again!!