In a small saucepan, over medium heat, warm the vinegar. Add the raisins. Turn off heat; let plump.
In a large skillet, fry the bacon until crisp, about 7 minutes. Reserve the drippings.
Cut any large sprouts in half. Place the sprouts on a baking sheet or in an ovenproof pan. Toss with the oil, 2 tablespoons of the bacon drippings, the salt, and pepper. Roast, stirring once, for about 30 minutes.
Meanwhile, cook the onion in the remaining drippings over medium heat for 5 to 7 minutes. Sprinkle the sprouts with the onions, crumbled bacon, and plumped raisins.
Make Ahead: Trim the Brussels sprouts a couple of days in advance, and refrigerate them in an unsealed plastic bag. Cook the bacon and onion up to several hours before serving.