E39 Fuse 15 and Battery Light

[Gemer]

Ladies and Gentlemen, I may have a quite complicated problem in which I'm lost.
1996/03 BMW E39 523i M52B25

I will try to describe it briefly

Years ago alternator died, got rebuilt and put in again, soon some anomalies* happened (after turning off the engine, one time random Powerup and finally turning off). The anomalies didn't last long, because Fuse 15 got blown, Battery Light came on. Later we discovered the Oil Levelling Sensor was faulty, next oil change we replaced it, Fuse 15 blew and Battery Light on again.
I've driven it for years now in this condition, with absolutely no problems, only the Battery Light annoys me.
(Built in voltage meter reads 14.7V, Multimeter reads 14.2V so it should be fine.)

by anomaly I mean: when I turn off the car completely lights, headlights, radio, AC and fan turns off and then on for like 1 second, then turns off completely
If I'm fast enough I can even pull out the key and it does the anomaly with the key in my hand .
by Fuse 15 I mean the 15th fuse in the glovebox.

A month ago I tried to get to the end of it.
Disconnected the Oil Levelling Sensor and put a new fuse to Fuse 15, Battery Light disappears, anomalies returned. Suspecting the Voltage Regulator, I quickly replaced it with a new TruckTec one, it seemed working, the anomalies were now different, instead of random Powerup and down, it just stayed on for like 1 more second.
I drove it for a week, Voltage Regulator died (can't blame it, BMWs mostly work with OEM parts). Thought it was the alternator so I got a working one with a genuine Regulator from my friend, installed it, working fine, but the anomalies I first detailed have returned.

Searched everywhere for weeks now, I can't find the answer for my problem.
I'm going insane ovet it.

Thanks for your helps in advance

[shogun]

Moved from Forum Software Questions & Suggestions to E39 forum.

[Zirconocene]

I can only give you some very general things to think about as you start to dig into this more, and even then, this is mostly from my experience on other German cars, not BMWs specifically, so if there is BMW-specific weirdness in how they approach their electrical wiring, please disregard all of what I've said.

Your car is operating on 2 distinct power circuits: switched and unswitched power. Unswitched power is typically taken directly from the battery and/or alternator and is intended to be available at all times. Switched power is what it says, and those circuits typically only activate when certain conditions are met but, at the most basic level, the switched circuit in the car starts when you turn the key in the ignition switch.

Given that you are experiencing electrical weirdness on components that are on the switched circuit, I would start with investigating that part of your wiring, if not the ignition switch itself. For example, do you know of any work that has been done for something like a stereo, that has disturbed the original switched circuit? What about a visual inspection of the wiring leading to the ignition switch itself?

That's where I'd start, not at the alternator (even though this is manifesting itself as a problem there, eventually).

Good luck

[jicaino]

I would suspect that on the first alternator blow up you had a short and there's a couple of wires fused together. I have an early 523i so if you need relevant or specific things let me know

[Gemer]

Thanks for the advice, I'll start looking into the ignition switch, that's one thing I haven't looked at.

[Gemer]

I could talk about it for a day
I figured out that Fuse 15 goes both to the Voltage Regulator and the Oil Levelling Sensor (tiny green wire). After first generator rebuild and reinstall, Oil Levelling Sensor got shorted out, died of shame, and blew Fuse 15, next oil change, we replaced the sensor (aftermarket Meat&Doria) first 10 kms, it died, Fuse 15 blew again.

I tried unplugging the faulty sensor, and driving it like that, that worked, Fuse 15 stayed on, Battery Light gone, Powerup and down anomaly returned when I turned off the car.
Next step I unplugged the Voltage Regulator, anomalies gone, Fuse 15 was good, BUT Battery Light was visible, very dim but visible, even a bit vibrating.

And thats where I left off.

I even took out the seats, to check all the wiring, but I found nothing.

And may I ask, for wiring diagrams or source for it? Couldn't find for M52B25, that would help a lot.

[jicaino]

I could talk about it for a day
I figured out that Fuse 15 goes both to the Voltage Regulator and the Oil Levelling Sensor (tiny green wire). After first generator rebuild and reinstall, Oil Levelling Sensor got shorted out, died of shame, and blew Fuse 15, next oil change, we replaced the sensor (aftermarket Meat&Doria) first 10 kms, it died, Fuse 15 blew again.

I tried unplugging the faulty sensor, and driving it like that, that worked, Fuse 15 stayed on, Battery Light gone, Powerup and down anomaly returned when I turned off the car.
Next step I unplugged the Voltage Regulator, anomalies gone, Fuse 15 was good, BUT Battery Light was visible, very dim but visible, even a bit vibrating.

And thats where I left off.

I even took out the seats, to check all the wiring, but I found nothing.

And may I ask, for wiring diagrams or source for it? Couldn't find for M52B25, that would help a lot.

That's why I told you you had 2 wires melted together, lol.
Send me your email and I'll send you an invitation to a site where you can access all tech, wiring and repair information on almost all chassis from bmw since the e34 on.