Since you have been inside everything I presumed you knew what everything was doing.
The blower regulator connects the negative side of the blower motor to ground. The possitive side is switched by the key and always battery voltage.
Check blower positive, is it 12+v. Check blower negative, it should be between 6v and almost zero volts. Theoretical would be zero at high blow. Hook your blower negative up with a jumper to ground and see if it blows. If it blows and you aren't getting air inside I don't know what you got.
There is a three wire connector on the firewall that allows some of the testing to be done without total disassembly. Must has been writen in the archives about this testing. I wouldn't think of doing this without a wiring diagram. If not, I might wind up buying a blower and regulator and a bunch of not needed parts.
Bosch Master, ASE Master, L1
33 years MB technician