Defender 300tdi alternator puzzle

HECKFLOSSE · Dec 1, 2015

I have had charging problems with our '95 Defender.
The warning light would flicker and charging was poor so fitted a new alternator today.
Now it charges at a lovely 14.5V- but the light is permanently on.

Is this a known problem?
I'm thinking dodgy block connector or some other wiring fault.
It hasn't got twin sockets or split charging as far as I can see.

Bit new to Defenders, so any advice is most welcome.
Cheers,
Jim

trax · Dec 1, 2015

check you've wired it up correctly.

it works by sending current down the thin wire to charge field coils. when alt is running it sends current up and they cancel out turning the light off.

so, pull the thin one from the dash and stick your multi on it with the ign off. should be 0 and not lit.

do it with ign on - should be 12ish.

touch it to earth.. should be lit.

if that works and it's still on, then it's probably a voltage difference between alt and battery. does it get dimmer or brighter when revved?

HECKFLOSSE · Dec 1, 2015

trax said:
check you've wired it up correctly.

it works by sending current down the thin wire to charge field coils. when alt is running it sends current up and they cancel out turning the light off.

so, pull the thin one from the dash and stick your multi on it with the ign off. should be 0 and not lit.

do it with ign on - should be 12ish.

Thanks for the reply.
There are two wires to the alt.
Batt and WL.
Will double check but they are different size threads so pretty sure they are good.
Light glows steadily irrespective of whether it is revved or how much load is put on the battery.
Will have a wiggle behind the dash. I suspect the wiring is not 100%.

touch it to earth.. should be lit.

if that works and it's still on, then it's probably a voltage difference between alt and battery. does it get dimmer or brighter when revved?[

trax · Dec 1, 2015

oh and if you had charging issues, you should really trickle charge your battery up. it may just be low on juice still and causing the issue

HECKFLOSSE · Dec 1, 2015

trax said:
oh and if you had charging issues, you should really trickle charge your battery up. it may just be low on juice still and causing the issue

It was dead flat, so I charged it slowly for 24hrs at under 4A.
Could still be low though it started a cold engine ok.
Carried out the 3 checks above, all ok.
So, a difference between Batt and Alternator voltages seems the culprit.
needs a run later to collect the kids, will try it after that.
Thanks for your help!
Jim.

jamesmartin · Dec 1, 2015

thin wire need to go to d+ terminal
thick wire to b+terminal
w terminal is for rev counter if fitted

HECKFLOSSE · Dec 10, 2015

Finally got to the bottom of this.
After checking through the wiring, I looked again at the alternator.
This is a non genuine equivalent that fits other applications..
It also has a choice of the old Lucas Three in a Row type of terminals or two insulated posts (as per my Defender original)
So, connecting my warning light wire to the thinnest lucar terminal seemed a worthwhile bet.
It worked.
Charging fine, light goes out when running, another job crossed off the infinite list!
Thanks for the ideas. Sometimes you just have to think sideways.
Jim.

Defender 300tdi alternator puzzle

HECKFLOSSE

Active Member

trax

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HECKFLOSSE

Active Member

trax

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HECKFLOSSE

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jamesmartin

Well-Known Member

HECKFLOSSE

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