In article ,
wrote:
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?

Depends how modern and complex. Some have alternators under the control of
the engine ECU.

If a more basic self contained unit, the norm is 12v from the battery goes
to the warning light, and the ground side of that to the alternator
regulator. Without that 12v, the alternator won't start charging.
Effectively that alternator connection supplies a ground to the warning
light engine stopped, which moves to +12v as the alternator starts
charging, so the light goes out.

--
*A snooze button is a poor substitute for no alarm clock at all *

Dave Plowman London SW
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