When I start the car, the battery light is off. Within 10 seconds, I hear what sounds like a relay and the battery light comes on. My meter shows the alternator is charging and battery is fine.
On earlier charging systems that used a separate voltage regulator some used a separate unit to control the ignition light and this might be the trouble - check with a wiring diagram.
If it is a an integrated regulator type the warning light wire connects directly to the alternator and all it does is ground the earthy side of the battery light through the rotor winding until the regulator begins to energise the rotor via the auxiliary diodes.
With smart charging systems and probably with later CANbus systems the battery light is controlled by black boxes.
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