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View Full Version : Alternator not charging, no D+ voltage



Tiptronik
01-29-2006, 05:19 PM
1995 BMW 318
My charging light came on recently and of course, the alternator stopped charging. I knew my alternator was due for replacement, so I pulled it out, put a rebuilt alternator in and thought all was good. I did a load test on the charging system, but no output on the alternator. Checked the alternator wiring and I have 12 Volts at the B+ terminal, but with the key on I don't have 12 Volts at the D+ terminal. I know that the blue wire eventually makes its way to the charge lamp in the dash, but has anyone run into this before? It seems to indicate some sort of short on the blue wire but the wiring diagram shows the D+ wire going from the alternator, it T's off to the data link connector, T's off to the climate control and then makes it's way to the dash. I've tried searching for this problem but found nothing on the 318's.

Does anyone know the path that the blue wire takes or of any known wiring problems with the alternators with these cars?

Tiptronik
01-29-2006, 06:08 PM
No one? :confused

Has anyone traced the blue wire from the back of the alternator before?

Tiptronik
01-29-2006, 06:46 PM
Ok, so everything is working again -charging again at 14.4 Volts.
I narrowed it down to what is called the Uncoupling diode. Don't know where it is, but it "uncoupled", then recoupled and the alternator started working again.
Not sure if this info helps anyone, but I'll attach a wiring diagram and hopefully someone someday can tell me where that diode resides.

143409

edg093
02-02-2013, 01:31 PM
Ok, so everything is working again -charging again at 14.4 Volts.
I narrowed it down to what is called the Uncoupling diode. Don't know where it is, but it "uncoupled", then recoupled and the alternator started working again.
Not sure if this info helps anyone, but I'll attach a wiring diagram and hopefully someone someday can tell me where that diode resides.

143409

where is the uncoupling diode located