Matty p · May 9, 2023

Good evening all I have had a look for a thread related to this issue but can't find anything,so here goes. I am coming to the end of my defender 90 300tdi build,when starting,the ignition light comes on (battery light) but does not go out when started. If I bridge b+ and d+ it charges at 14.5v and the battery light goes out,likewise, if I put a feed to the warning light when the engine is running the same also happens. There is two brown/yellow wires at the dash,I'm guessing one goes to the alternator and i think the other goes to a white wire with inline resistor. Does anyone have any ideas please? I will be very grateful. Thanks, Matt

marjon · May 9, 2023

You need @mystery

Did I miss pics in a Fred somwhere?

J

Matty p · May 9, 2023

marjon said:
You need @mystery

Did I miss pics in a Fred somwhere?

J

Sorry no pics I'm afraid.

marjon · May 9, 2023

No worries, all fixable when the good guys arrive

.

J

Matty p · May 9, 2023

marjon said:
No worries, all fixable when the good guys arrive .

J

Hopefully someone will have an idea, im just about at my wits end!

mystery · May 10, 2023

may help

Matty p · May 10, 2023

Thanks Mystery, i do have have something very similar too thanks. Going to have another play this evening.

discool · May 10, 2023

Matty p said:
Hopefully someone will have an idea, im just about at my wits end!

So your vehicles battery isn’t charging then ? then an iffy alternator regulator pack is a possibility.
Wiring diagrams won’t tell u that but testing will

v8250 · May 10, 2023

@Matty p , this may help you to understand alternator ccts a little more...they're very simple to fault find and fix https://www.howacarworks.com/ignition-system/troubleshooting-the-ignition-warning-light

Matty p · May 10, 2023

Hi all and thanks for your help,much appreciated. I am writing this from the front seat of my 90 still trying to work out what feeds the brown/yellow at the bulb to put it out when running and also excite the alternator? If i put my power probe at brown/yellow and give it 12v when running, the light goes out and charges normally. Im almost bald already but this will finish it off i think!!!

kermit_rr · May 10, 2023

B+ is normally the battery positive, sometimes you'll see D+ as the battery positive, depending on the make. Never seen both on the same unit before
W is usually for the engine RPM signal. If that helps

kermit_rr · May 10, 2023

Alternator Terminals Explained - Conquerall Electrical Ltd

Alternator Terminals Explained-If you've ever wondered what all the connections on your alternator do, you've come to the right place. In this article,

conquerallelectrical.ca

The B+ terminal is the actual high-current output, and the D+ terminal is a duplicate of the B+ terminal. The D+ diodes have lower current ratings. The B+ and D+ terminals are connected through the same set of windings on the alternator.

Matty p · May 10, 2023

Thanks Kermit,my alternator has b+ battery/starter cable,d+ field coil exciter and warning lamp, white wire for rev counter i believe.

Matty p · May 10, 2023

The alternator has to be okay I'm guessing because it charges fine when the d+ is excited (12v). Its just a case of finding the missing feed(i think).

kermit_rr · May 10, 2023

Matty p said:
Thanks Kermit,my alternator has b+ battery/starter cable,d+ field coil exciter and warning lamp, white wire for rev counter i believe.

Ok, so B+ to the battery, charge warning to D+...
You say the light comes on, do get 12v to the wire that connects to D+ with the ignition on? Is there a good earth?

Matty p · May 10, 2023

So with the d+ wire disconnected from the alternator,there is 12v at the terminal. Once the terminal is back on the alternator and engine running it measures approximately 2v,obviously not enough to excite the field coils. It seems like a poor connection maybe? I just cant find where the 12v comes from.

kermit_rr · May 10, 2023

Matty p said:
So with the d+ wire disconnected from the alternator,there is 12v at the terminal. Once the terminal is back on the alternator and engine running it measures approximately 2v,obviously not enough to excite the field coils. It seems like a poor connection maybe? I just cant find where the 12v comes from.

I think it's a thin brown wire, should be pretty obvious

Matty p · May 10, 2023

What i mean is where does the 12v originate from to feed the circuit? I also know there is a resistor and a diode in the circuit behind the dash but not sure if these would cause the issue.

kermit_rr · May 10, 2023

Sorry. It should be a switched live off the ignition. I don't have the details for your motor.

When you bridged the B and D, did the ignition light go out? I assume not? If the signal wire isn't getting 12v but the day light is on then I'd be looking at whatever is behind the dash.. possibly a diode problem

Matty p · May 11, 2023

Cheers Kermit, I was thinking along the same lines regarding the diode. When b and d are bridged the light goes out and charges normally. I think for the cost of it I might as well just change the diode just piece of mind.

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