Sprinkle ribs with salt and pepper. Place in slow cooker. Cover with onion slices.
Mix remaining ingredients; pour over ribs and onion. Cover and cook on low heat for 8-10 hours.
Remove ribs to warm platter; keep warm. Strain juices.
Pour juices from slow cooker into 1 quart saucepan. Heat to boiling over medium high heat; reduce heat to medium. Cook about 5 minutes or until sauce has slightly thickened.