Combine first 4 ingredients in a small saucepan; cook over medium heat until smooth, stirring often. Cut ham in half lengthwise. Slice each half horizontally into 2 (1/4-inch-thick) slices.
Coat grill rack with cooking spray; place on grill over medium-hot coals (350° to 400°). Baste ham with jelly mixture; place on grill. Grill, covered, 3 to 4 minutes on each side or until ham is thoroughly heated, basting with remaining jelly mixture.