You have a lazy diode pack, that is why you have to rev a bit, should not need to at all.
Make sure your terminal marked "IGN" is nice and clean, and that you have the CORRECT wattage bulb in that works ok.
It uses the ignition light(battery) to feed LIVE to the alternator to initiate the charging process, once running, this terminal(IGN) then goes positive as the alternator starts to charge so extinguishing the warning light sas two lives don't make a bulb work!!
tabetha