The one-time goalkeeping coach at Manchester United will assist Harford, who was appointed caretaker boss after Paul Harts departure, with first team coaching.
"Mick and I are very good friends," said Coton.
"We have kept in touch over the years. We normally speak two or three times a week and we have the same philosophies on how the game should be played.
"He called me and said he needed a hand and wanted someone he can trust who he gets on well with.
"This was a big decision for me because I live up in Bolton with my family. But we go back a long way and I am delighted to be here to help."