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Short answer, the regulator is failing. As eagle and Anteek29 say, your voltage is too low.
9 amps at 6.57V is probably normal for original wiring, ammeter reads coil current as well as battery. If FSB 11/29 has been applied, then the needle will stay close to center, is it reads only battery charge of 1-2 amps.
With headlights on, the alternator is not providing enough current, low beams it barely keeps up, high beams are discharging the battery.
You can live with this situation by using original 21/21 CP bulbs, but the alternator needs a new regulator inside.