Alternator warning light fault

Hi I have a 1995 autobiography I am restoring, I have a fault on the alternator warning light, when the ignition is turned on the warning light does not light up, bulb is good and print circuit board on dash panel looks ok. If a test lamp is put between to warning light connection on the alternator and battery live it lights up and goes out as soon as the engine is started. The alternator is putting out 14v so all seem ok with the alternator. all connections are clean. I am guessing there is some rely or other electrical wizardry between the alternator warning light connection and the warning light. Of course the BeCM no doubt has a hand in things, does anybody have any suggestions?

Thanks Chrisn

Trust you have RAVE!

The warning lamp wiring will be in there, take a gander and you should see where it is fed from.

assuming it's a P38 from your mention of the BECM, The alternator warning light, unusually is not fed from the D+ on the alternator, instead it goes via the BECM. So it's alternator to BECM, then BECM to dash light.
As Saint said, RAVE will give you the connector & pin numbers.

Thanks I had not heard of RAVE first Range Rover I have restored I'm more used to Mini's & Yanks things with basic electrics that can be started with one piece of wire if things go wrong. I am downloading
Chrisn

You're going to be learning a lot about electrics then!

Grrrrrr said:

You're going to be learning a lot about electrics then!

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as well as pulling your hair out screaming and getting very frustated

Thanks for the encouragement guys!!! well I now have RAVE and all the circuits check out and seem to be working ok, if the warning light connection on the alternator is put to earth (ignition on engine not running) the charge light lights up as it should. which I assume would suggest an alternator diode fault. I have tried a second hand alternator and it reacts exactly the same, could it be possible both alternators have the same fault? or is this something else???
Thanks Chrisn.

before you condemn alt check for bcem plug corrosion as this is known to cause reported fault

chrisn said:

Thanks for the encouragement guys!!! well I now have RAVE and all the circuits check out and seem to be working ok, if the warning light connection on the alternator is put to earth (ignition on engine not running) the charge light lights up as it should. which I assume would suggest an alternator diode fault. I have tried a second hand alternator and it reacts exactly the same, could it be possible both alternators have the same fault? or is this something else???
Thanks Chrisn.

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Check the earth bonding strap from the engine to the chassis, if the light comes on when you earth the D+ wire, that eliminates the BECM. You can also try an earth wire from the alternator housing to the battery negative.

remote chance, but on the bottom of the large bracket the alternator bolts to is an earth strap that leads up to an earth stud by the brake hydraulic pump...check this too.

Thanks again, if D+ is earthed (to 12v - ) the warning light comes on, it does not come on if the alternator body is earthed. This to me suggests that the warning light circuit is not getting its 12v neg supply (engine not running ignition on) as it should through the alternator windings. (I think) so all seem to suggests I have two alternators with the same rare fault , Would you agree?

chrisn said:

Thanks again, if D+ is earthed (to 12v - ) the warning light comes on, it does not come on if the alternator body is earthed. This to me suggests that the warning light circuit is not getting its 12v neg supply (engine not running ignition on) as it should through the alternator windings. (I think) so all seem to suggests I have two alternators with the same rare fault , Would you agree?

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It does sound that way and the fault is not that rare. Diode pack failure or brushes.
If you can borrow a known good alternator, you can check before you put it on the car, you can also check your spare alternator with a small bulb connected to the D+ and battery positive and the alternator case to battery negative, if the bulb lights the alternator is OK.

Hi thanks for the advice, fault turned out to be a faulty voltage regulator 15 quid off ebay and problem solved. But no doubt there will be many more to come!!!!

Mine has been doing that since 97....... and still duz, it reminds me to fix it lol