Okay,

1994 Disco tdi......

I made the grave mistak of letting the wife use the disco last night to nip out....errrrrrr

when she got back she said "does your battery light always stay on?"....my answer "no"

I went outside to check.....and yes the alternator light was on..........BUT it is on with the engine & ignition OFF ???

once the ign is turned on to stage one it goes off (when I would expect it to be on)

So the problem is...my alternator light stays on when the car & ignition is off (with the doors locked and everything)

What I have quickly done: disconnect the battery - light goes out..reconnect, light on...

disconnect the alternator 'live' light out....connect back on..I cleaned all the contacts on the alternator..no change...currently run out time to fault find..have my little sisters wedding tomorrow then travelling for the next two weeks........

Anybody have ANY thoughts where I should start looking to track the issue...

Thanks

H

could be the diode or reg pack inside the alt. theres a permanent live wire from the battery to the alt, and this maybe being "switched" to your warning light?

I suspect a faulty alternator but one thing to check before parting with your hard earned and that is to check to make sure the charge warning wire isn't shorted to another wire or live feed. Chances are, its shorted inside the alternator.

Charge warning light works like this.......... with the ign on, a 12v feed is sent to the bulb, the bulb earths via the alternator. When the engine is started, alternator voltage is sent from the alternator to the light, since this voltage is higher (about 14v) than the voltage going to the light on the ign side, this makes the light go out, if alternator voltage drops below battery voltage, the light is able to earth at the alternator causing it to illuminate, if the alternator overcharges (by a considerable amount, say, 19v), the opposite happens, basically two differing voltages pushing against each other. If your charge warning wire is shorted somewhere, in your case to a positive, the light will come on when the engine is off, if its shorted to ground, the light will come on when the engine is running.

A good description of how the light works. This also means that if your battery voltage and alternator voltage go down together, the light will not come on. This happened to me (on an Audi) when the brushes got worn. Eventually the engine just stopped...

this sounds exactly like what happened to my 94 200tdi (funnily enough also while the woman was driving it). It lasted a couple of days before the battery was totally dead. I needed a new alternator - well, I got a new alternator but whether I NEEDED it, I'll never know!