Well a manual circuit should be pretty trivial as current will flow down a
wire in one direction and in the other when its discharging. They used to
fit meters with a centre 0 and you could then tell exactly what was going on
and when.
Brian

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The Sofa of Brian Gaff...

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Hi All,

Back in the dark ages (60s,70s, 80s) cars had little bulbs that would come
on to tell you your battery was no longer charging.

There have been a few people on the Peugeot'007 self
Help FB group I'm on whose alternators have died, but their car's not
charging light hasn't illuminated (despite its passing its POST before the
problem and after its been rectified (see what I did there).

Got me to thinking, how were these bulbs driven in the past (i.e, what
electrics / electronics / circuit lit them when charging stopped)?

And how are they supposed to work in "modern" Cars?

On the '007, I believe it's an LED and I SUSPECT it's fed from the ECU??

Anyone know?