Easier yet. Start the car. Turn on all accessories including the A/C, headlights, rear window defroster, radio, wipers. Then measure the voltage. If its 14 or so, then alternator is providing enough power. If its less, then the alternator is weak. The light is turned on by the regulator circuit on the alternator itself. It is possible that it is malfunctioning. As long as the alt is making power, you can learn to live with it, disconnect the bulb or wire, or replace the alt. Of course without thtat light, if the alt should actually break, you won't have any indication other than a slow start or dim headlights, etc.