Battery warning light on with ignition off Help

[Algeroth79]

I got a 1990 325is
Monday morning had all the lights in the cluster light up Monday after work Head lights were dim wipres moving slow.
Tuesday got battery tested and it failed got new one. checked alternator and it was low voltage so I took it out had it tested and it failed. Bought new one. it the dreaded Atozone rebuild but I tested it after the install and it outputs 13.5 Volts at 1500 RPM with everything on.
Now the Battery warning light comes on after I turn the ignition switch off.
Battery was dead next morning. Jump started the car drove 25 miles. Light did not come on during the drive but right after I switched the ignition off there it was.
I have been disconnecting the battery between drives for now. I'm going to check my ignition switch this weekend but if anybody else has any other suggestions I'm open to them

thanks

[jlevie]

Check the writing diagrams to be sure, but as i recall the battery warning light is fed switched power. So if the light is on with the ignition off, either something (switch or improperly installed aftermarket electronics) is supplying power to the cluster or there's a fault in the alternator that is back feeding the warning light. Since this problem apparently didn't exist before the alternator swap, I lean toward it being a bad alternator. A quick check would be to disconnect the alternator output lead. If the light goes out, the alternator is bad.

[StereoInstaller1]

Feedback through the light: incorrect field wiring. Page 1230-1 of the ETM shows the diagram.


Since there is only 1 plug and 1 terminal, there isn't too much to fuck up, is there?

I say bad alternator. Incorrect diode is my guess, but who knows.

Test like this: leave battery connected, unplug that little plug, see if light goes off, see if alternator stays warm half an hour later (which it will now) and prepare to bitch at otterzone.

[StereoInstaller1]

there's a fault in the alternator that is back feeding the warning light. Since this problem apparently didn't exist before the alternator swap, I lean toward it being a bad alternator.

Twisted minds think alike, huh?

[DJB]

Either the field supply wire is connected to the battery feed terminal, or two (likely more) diodes in the alternator have melted and are now conductors.

The detail that the battery was dead the next morning points to bad diodes.

Yes, rebuilds are a dice roll. It's better to replace the brushes or voltage regulator on your original one than gamble on buying someone else's problem. The core might have just had a bad VR or bearing that was replaced during the rebuild, or it could have bad windings or intermittent diodes that were missed during the (minimal) testing.

[Algeroth79]

ok I will pick up a new alternator tomorrow. before I rip apart the Steering wheel
will post when done.

[thehapakid]

I just had this problem today and it turned out that my alternator was bad.

After turning off the car, the battery light was still illuminated. I came back to it about 3 hours later and I couldn't crank it over. I got a jump start and drove it to the shop and it was diagnosed as an alternator failure.

[Algeroth79]

Yup that was the problem. Just got the replacement one and no light thanks guys for saving me from taking the steering wheel out.