The 59-year-old spent last season at the Daggers under boss John Still, whom he worked with at Luton.
Harris has become Wood boss Luke Garrard's number two on an undisclosed-length contract.
"I can bring experience with me because I have been very fortunate during my time with John Still," Harris said.
He added to the club's official website: "If you are a number two then you are the eyes and ears of the players and you certainly have an input into the coaching side and an input into the game management side and, as I said, I have been fortunate in the clubs that I have been with.
"With Dagenham, for instance, we got out of the Ryman league and then we got out of the Conference, as it called then, and we then took Dagenham into League One in the Play-off final against Rotherham."
National League side Boreham Wood have named former Luton, Stevenage and Dagenham coach Terry Harris as the club's new assistant manager.