I’ve experienced something like that and issues was the pedal travel. Pull on the brake pedal to see if the light comes on.
Actually, it's more likely that the brake lights won't turn OFF if the pedal isn't all the way up. But the switch itself can freeze up so the lever doesn't move or the contacts get corroded. It'll be a two person operation to replace, as it's secured by two screws from inside the cab. One to hold it in place while the other turns the screws after the floor mat has been pulled back.
