SimonJ

"VeryYellow" <alan.hancock@casservicesltd.com> wrote in message
news:1121797946.656867.266730@g44g2000cwa.googlegroups.com...
Hi

This morning my wife's Disco (92 200Tdi) battery was flat as it could
be. I dumped by Defender battery in to get her to work, all seemed ok.
When she got to work and turned the ignition off, the battery warning
light came on (with the key removed!), she left it like that all day,
started the engine first time and drove home.
Now I have a Disco with the warning light on all the time the ignition
is off, and when I turn the key to the point where the dash lights go
on the battery light goes out! the light stays out when the engine is
running and the battery seems to charge (or at least its not flat yet
and seems to have plenty of power).
REALLY lost on this one, is it a new alternator? Any clues?
Expecting an early start swapping batteries tomorrow. ?


It is a fault in the regulator, the diodes (or one of them at least) that
are supposed to prevent the current flowing from the battery connection, to
the rotor, have gone short circuit, so your rotor is always live, rather
than just being live when the ignition is on. This means that the charge
light will be getting a backfeed from the rotor. When the ignition is off it
is earthing itself through the rest of the ignition circuit. When you switch
the ignition on, the battery light has live on both sides of it, so it goes
out. It will still charge ok, but as you have noticed, it will flatten the
battery if left.