Rinse grapes and then insert toothpicks or skewers into the stem end of the grape. Set on a paper towel and set aside.
In a heavy bottom saucepan, combine the sugar, water, and corn syrup and bring to a boil over medium-high heat. Keep a rolling boil, stirring frequently. Boil for about 5 minutes to reach the right temperature. Use a thermometer and get the syrup to 300 F.
Carefully dip each grape into the syrup, moving it quickly to cover all the sides of the grape. Next, roll the grape in the crushed Jolly Ranchers.
Set aside on parchment paper and let rest for 30 minutes. Carefully remove the toothpicks and enjoy.