Heat grill to medium-high heat. Make Dressing. Whisk together vinegar, sugar and mustard. While whisking, add oil in a thin stream. Whisk in basil, salt and pepper.
Pasta Salad. Heat a pot of lightly salted water to boiling. Add pasta; cook 7 minutes. Drain and transfer to a large bowl. Toss with half the dressing.
Secure onion slices with toothpicks. Grill onion and peppers for 10 to 12 minutes, turning. Remove toothpicks and chop veggies. Stir into pasta. Reduce grill temp to medium.
Grill sausages on medium heat or the cooler part of a charcoal grill for 9 to 10 minutes, turning often, until internal temperature registers 150° F. Slice into coins. Toss with pasta, salt, peppers, onions and remaining dressing.