Your "now nothing" means your blower burned itself?
What happens with your used one. It get burned too?
"Just no blower unless I'm going 40 mph" means it get on after 40 MPH?

If you apply 12V direct to the blower, does it works?
If yes, disconnect the plug to the blower. Do you get 12v on it?(car's plug) (pushing the "max" button)
What about the relay?

Start with this. Let us know.