Defender 300tdi battery warning light

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

You need @mystery

Did I miss pics in a Fred somwhere?

J

marjon said:

You need @mystery

Did I miss pics in a Fred somwhere?

J

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Sorry no pics I'm afraid.

No worries, all fixable when the good guys arrive .

J

marjon said:

No worries, all fixable when the good guys arrive .

J

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

may help

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

Matty p said:

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

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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

@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

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!!!

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

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.

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

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).

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.

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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?

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.

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.

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

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.

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

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.