I was just going to start a new post on this, but I think that I'll add onto yours. We're camping now, but on Friday I pressed the button and nada! Got out the test light, and started tracing. Power to the switch, and pressing the switch indicated that the issue was elsewhere. Pulled the plastic cover off the motor and a little water came out. Pulled the 2 screws off the motor and pulled the cover off. When you do so, your pulling the magnets off and exposing the armature and brushes. It was wet with some rusty water. I cleaned out the best I could, removing the water, drying the brushes and put it back together and pressed the switch. Oops.... retract was now extend and extend was now retract. Remove the cover, rotate 180 and put it back. Success!
So... mark the top of the cover, pull it and check for water and clean things up. A little air would help, but I did it without it. Then put it back together and give it a shot.