Sorry to have missed this the first time around.
This is one of two things. Blower motor or blower control module. Realizing that I said blower motor and that when you give it 12V straight on that it fires up....yes it can be the blower motor. In the automatic cars the blower never gets full 12V from a dead stop. It is always ramped up in speed. Try operating it in normal mode with the blower on low or medium. Now tap the blower motor a few good times. Does it start?
If not, the power transistor on the BCM is most likely going bad. You could pull the BCM out, get the part off the transistor, solder a new one on and be set or hit up a JY and get a different BCM for $10-$20.
Then you can take the rigged up power lead going throught the firewall out of the loop. Putting a power wire with that much power through the firewall could become a fire hazard unless it is very well insulated and a rubber grommet was used to keep any chafing or rubbing from occuring.
It would be an awful day if something happened to your car because of this temporary fix.
00 Regal GS: All kinds of cool stuff.