Obviously, I don't know why the old worked and the new doesn't, but I've had the problem of spark plug wires blowing off my 1973 3 cylinder gas engine Ford 2000 in the past. Every time it is was because compression was getting past the spark plug and blowing the wire off. I've re-torqued the spark plugs and it has fixed the problem every time.
BTDT is meant to be an abbreviation for "Been there, done that". Sorry for the confusion.
Good luck with your troubleshooting.
Tom in TN