Harrison was in charge of the David Beckham generation at United.
He says Ferguson has a simple philosophy when it comes to recruiting players at Academy level.
"Something he used to say to parents when trying to get them to sign was there's three things he'd promise," revealed Harrison to manutd.com.
"1) They'd get a good apprenticeship. 2) If they're good enough, they'll play in the first team. 3) If they're not good enough, he'll find them a club so they can have a career in the game. He's never let anyone down in that respect."