Place the sausages in a large pan. Pour the red wine over the sausages. Add the garlic, onions, and parsley. Drizzle the olive oil over the mixture, making sure everything is evenly coated. Marinate for 24 hours in the refrigerator.
Preheat the grill to medium heat.
When the grill is hot, add the sausages and cook, turning occasionally, until cooked through, about 10 to 12 minutes.