I have a LeSabre, but cannot help you very much.  I don't think your engine is bad, though.

Is it snowing at your place [i]right now?[/i]  It is here.

You can test the motor by touching the wires directly to the battery for a second. There should be at least one positive or else there is no way it can operate.

If it is not a bad fuse, it might be a melted wire socket. I think you have the same engine as my piece o crap Mustang, 3.8l. Mercury Lesabre right? The electrical system on these cars are total crap. They run way to much juice through the wires. What happens is that they heat up and slowly melt and various wire sockets connected to them. I had a problem with my electrical radiator fan. I changed all the heat sensors, nothing... replaced all the wires going to the motor, nothing... I traced down the problem to a bad circuit board with a melted socket connector. They are located under the drivers side dash. I had to change the circuit board and splice in a new 12 wire socket group. Pain in the ass!

I forgot to add, there is about 70 feet of vacuum hoses on these cars. The heater/AC systems for some strange reason are interconnected with these hoses. Check all your vacuum system for leaky hoses or broken connectors. I couldn't figure out why I couldn't change my vent settings, I only could get the defroster to push air. I changed like 50+ feet of hose, then on the last piece of hose connected to the AC throttle kicker, bam! I got my fan controls back. I thought it was really wierd that the carburator is connected directly to the heater/AC?

One shot,
kind of mixed advice today.
As sodie said check to see if you run hot 12v to the terminal on the blower makes it run, it it does, then check on top of the AC/Heater housing for a 2x3 size plate held by a couple of screws. It will have a wire connector with IIRC 4 wires. When you get this thing off, look at the other side of it the part that is inside. You should see a bunch of loops, these are the resisters that allow the different speeds. See if one or more are burned thru. This usually is the problem if others speeds still work.
If the blower doesn't work when you hot wire it, it needs to be replaced. You can get these at any large auto supply store should cost about $35 for the new blower.