How Is Energy Consumption Moderated In A Car?

Car question. When I turn on my windshield wipers, the energy for those two step motors comes from the battery. And it comes to the battery from the gas tank via the alternator. This means that if I drive with my wipers on, I will run out of gas sooner. But doesn’t the alternator constantly attempt to charge the battery? Where is the “switch” that allows the alternator to suck less energy out of the tank when I turn off my wipers? I imagine something like a bicycle dynamo that can be either on the wheel, imposing drag, or off the wheel.