It may not be the harness that set him off. You say he was in a window sill when he attacked you? And he's not neutered?
There is a problem sometimes with cats called "redirected aggression". It's when a cat sees something it considers an enemy (a dog, another cat) that it can't reach and someone or something the cat used to like is closer. The cat redirects it's aggression from the object it can't reach, to the one it can (in this case, possibly you). :/
Unfortunately, knowing why it (might) be happening doesn't make it easier to get him back to liking you. You may have to start over as if you had just been introduced. This will be difficult, you will really want to touch him, push him to play, etc. Instead, ignore him. Maybe sit on the floor in the same room and read, but DON'T try to push him into coming to you. Let him be the first one to make a move. (You can cheat by putting a favorite stinky treat near you, but ignore him while he eats it. Move the treat closer day by day.) It takes a lot of patience to get a cat to change their mind about something, but it can be done.
Dr. Seuss~DLH (brother's cat)~June 2007-
Misty~DSH (my cat & Mooby's mom)-?- Sept. 15, 2014
MooBoots(Mooby) ~ DMH(Mom's cat)~July 21, 2008-
Sunshine~ Golden retriever X white german sheperd (Dad's dog)~October 24, 2008-