Hey guys I just tackled this problem so I thought I would post to help out a bit.
I have a 2003 Grand Prix GT
My symtoms were blower levels 1 and 2 not working with 3-5 working just fine.
It was very hard to get the three screws off the old resistor, I unscrewed the one...you will know what one I am talking about, it's the only one that is remotely easy to access. I then just slid the big base plate of the old one out from the two back screws. It came right out and the new one slid into place very easy and securally.
Here is a picture of my old one (on the left) and the new one (on the right)
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Here is a picture of the old one. Obviousally water got under the green cover destroying it.
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Forgot to mention I got the new one off of Ebay for $19
