The husks will char, but the kernels will steam, becoming tender and just lightly perfumed with smoke. Peel off all but one or two layers of husk.
Here's how to grill corn my way:
Peel away the outer layers of husk. If the ears have many layers of husk on them, I'll peel off the first few, leaving a few layers for protection, but allowing the kernels to see a little action.
Use a lively fire. I usually put the corn on the grill as soon as the initial flames from the charcoal (hardwood, not briquettes, please) die down and the coals are still red-hot. This way, I take advantage of all those Btus while waiting for the coals to settle down to the perfect temperature at which to grill meat or fish. Corn protected by its husk is very forgiving, so if a few flames lick the ears and light the husks, don't worry. Take care, however, not to crowd the grill, which would choke off too much air to the coals.
Keep turning those ears. Grill the corn, turning often, until the first layer of husk is completely charred. Depending on your fire, this could take from around 5 to 10 minutes. You can push the corn to a cooler spot if you're grilling other things for your meal, or transfer the grilled corn to a platter and keep it warm in the charred husks until serving.