Brown bratwurst in a nonstick pan.
Combine sauerkraut and onion in a greased 6-quart crock pot.
Place brats on top of sauerkraut.
Pour beer over brats. Cover crock pot and cook on LOW for 7 hours.
To makes sauce, stir together mayonnaise, chili sauce, ketchup, onion, pickle relish, and pepper in a small bowl. Refrigerate until needed.
Once brats are done, preheat oven to 350 degrees. Line the inside of buns with cheese, 2 slices per bun.
Place buns in oven until cheese is melted. Stuff buns with kraut/ onion mixture, draining off liquid first. Place a brat in each bun and top with dressing.