The blower rencently went out in my 1999 Grand Prix SE. I found a used one on ebay for about 44 bucks. Now that I have installed the new blower it only works on one speed and thats HI. What could cause this problem ?

Resistor

X2

Yep, resistor ( ~ $17.00 @ AutoZone )

Would the fact that the doner blower came for from a 2001 grand prix instead of a 1999 have any thing to fo with it working on just hi

Don't rule out the ignition switch. I replaced my blower motor resistor thinking that should solve the problem of the fans only working on high, but it didn't. Needs a new ignition switch. Just FYI.

lol, I opened this thread in hopes of seeing an m90 on a 3.1L.

It could be the problem. I think the blower motors varied slightly from 97-99, 00-01, and 02-03. Cannot guarantee that, but I remember seeing different ones because I had to replace my blower too. Try the resistor first though. Hope that helps