Remove and discard leg truss from turkey. Pull off and discard lumps of fat. Remove giblets and neck (reserve for other uses). Rinse bird well. Insert a meat thermometer straight down through the thickest part of the turkey breast to the bone.
On a charcoal barbecue (20 to 22 in. wide) with a lid, mound and ignite 60 charcoal briquets on firegrate. When coals are spotted with gray ash, in about 20 minutes, push equal portions to opposite sides of firegrate. Place a foil drip pan between mounds of coals. To each mound, add 5 briquets now and every 30 minutes during cooking. Set grill in place. Set turkey, breast up, on grill over drip pan. Cover barbecue and open vents.
On a gas barbecue (with at least 11 in. between indirect-heat burners), turn heat to high, close lid, and heat for about 10 minutes. Adjust gas for indirect cooking (heat parallel to sides of bird and not beneath) and set a metal or foil drip pan in center (not over direct heat). Set grill in place. Set turkey, breast up, on grill over drip pan. Close barbecue lid. If edges of turkey near heat begin to get too dark, slide folded strips of foil between bird and grill. Fat in drippings may flare when barbecue lid is opened; quench by pouring a little water into the pan.
In an oven, place turkey, breast up, on a V-shaped rack in a 12- by 17-inch roasting pan (or one that is at least 2 in. longer and wider than the bird). Roast in a 325° oven for 2-3 hours, or until thermometer reads 160°.
In a glass bowl or measuring cup, mix habanero marmalade and orange marmalade. Heat in a microwave oven at full power (100%), stirring once, until soft, about 40 seconds. Stir in sage. When breast temperature is about 135° for birds up to 18 pounds and 145° for those over 18 pounds (about 45 minutes before turkey is done), spread marmalade glaze all over turkey. Continue to cook until thermometer reaches 160°. If wing and leg tips start to get too dark, cover with foil.
Drain juices from cavity into drippings and reserve for easy gravy. Transfer turkey to a large platter; let rest 15 to 30 minutes before carving. Add salt to taste. Serve with easy gravy.
Nutritional analysis per 1/4 pound boned cooked turkey with skin, based on percentages of white and dark meat in an average bird.