[VetteVet]

Just some thoughts on this. I am curious if the resistance on the new regulator might be be too high to light the idiot light with the key on and engine off or any other non charge state. I would measure the ohms between the brown terminal and the regulator ground and compare that with the old one. I believe that the points are closed on that electromagnet and when the key is on(engine off) or the alternator isn't putting out volts the brown wire grounds through that and lights the charging light and when the engine starts the brown wire feeds the alternator field and the alternator output will open the regulator points and turn off the light. Anyways measure the resistance on the terminals to ground and compare them with the old one. There may be a difference between the years.
If the old one was overcharging then the points may have stuck on it and it wouldn't be an accurate comparison. Does the light come on with the harness plug disconnected?