Alternator not charging and battery lights stays on with engine running

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Thatclassicdiesel
Posts: 3
Joined: Feb 26, 2022 11:53 AM
Location: Missouri

Alternator not charging and battery lights stays on with engine running

Post by Thatclassicdiesel »

So I’ve been searching this forum for about two weeks now and have been able to make some progress on my issue but haven’t gotten it all figured out yet. So my car died going down the highway and I had my volt meter on hand and found that the battery was dead, got a jump and got it home. I was suspect of the v/r on the alternator so I ordered a replacement and it still wasn’t charging. I noticed that the blue wire going to d+ was unplugged and up to this point my battery light has not come on so I lengthened the wire and put on a new connector and once I did the battery light came on but won’t turbo off with the engine running and it only dims when I rev the car. I can however add 12v from the positive battery post to the d+ terminal and the alternator will charge at 13.8 volts at idle. Just found out today that my battery was the incorrect size and had a cell that was shorted out, the new battery did not make the light turn off. I’ve also checked the c101 connector for corrosion and found that pin 12 of the diagnostic connector does not have 12 volts but the wire going to d+ has 11.6.
RossDinan6
Posts: 79
Joined: Jun 24, 2006 11:23 AM

Re: Alternator not charging and battery lights stays on with engine running

Post by RossDinan6 »

I suspect low voltage to the D+ terminal. Since you are charging supplying 12v directly, you seem not to be getting that through the instrument cluster. Have a look at the voltage at that terminal with the car running.

I had an issue on my e24 where inside the cluster there was/were poor connections not allowing the regulator to be energized. In case you didn't know, the regulator gets ignition power through the battery indicator. A bad bulb or any bad connections between there and the alternator will prevent charging.
gadget73
Posts: 874
Joined: Nov 22, 2017 10:30 PM
Location: New Jersey

Re: Alternator not charging and battery lights stays on with engine running

Post by gadget73 »

Have the bulbs in the cluster been swapped for LED? I know someone that did that on another car and it caused this same problem. Not enough current flow through the lamp to the regulator caused it to not switch on and charge the battery.
Thatclassicdiesel
Posts: 3
Joined: Feb 26, 2022 11:53 AM
Location: Missouri

Re: Alternator not charging and battery lights stays on with engine running

Post by Thatclassicdiesel »

No, the are still incandescent bulbs.
gadget73
Posts: 874
Joined: Nov 22, 2017 10:30 PM
Location: New Jersey

Re: Alternator not charging and battery lights stays on with engine running

Post by gadget73 »

ok, fair enough. I just remember that thread went and went for way too long before that bit of information came out, then it all made sense.

Is the 11.6 at the D+ connector with it plugged in to the alternator? If thats unplugged, it sounds right for drop through the switch and lamp and such. If its at zero volts with it plugged in, either the lamp circuit is overly high resistance for whatever reason, or there is some problem with the alternator still. Might be worth having a look at pin 12 of the diag connector with the alternator plugged in vs unplugged to see if it changes. By the diagram the connection to the diag connector splices in directly at the alternator.
demetk
Posts: 8429
Joined: Aug 09, 2007 8:58 AM
Location: CT, USA

Re: Alternator not charging and battery lights stays on with engine running

Post by demetk »

Try a putting a bulb in series with that battery powered test wire you used and see if the bulb goes out.
Thatclassicdiesel
Posts: 3
Joined: Feb 26, 2022 11:53 AM
Location: Missouri

Re: Alternator not charging and battery lights stays on with engine running

Post by Thatclassicdiesel »

Well guys I figured it out, the reason that the D+ was not getting 12v was due to a burnt out fuse.
Replacing this fuse also fixed my cigarette lighter and power seats lol
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