Scales became part of the Wimbledon "Crazy Gang" that graced the top flight of English football and that won the FA Cup in the famous 1988 final. He played as a substitute in the final, though unusually playing as a forward after coming on for striker Terry Gibson. He made his debut for the club in a 1–0 First Division defeat to Watford, who had just appointed former Wimbledon boss Dave Bassett as their new manager, on 15 August 1987. He was soon a regular member of the side, and over the next seven years would make 240 league appearances for the club, scoring 11 goals, including five in the 1988–89 season.