You need to remove that cap and there should be a screw in there that you can remove that takes off the inside cover. Then there should be some more screws holding on the outside of the mirror under the cover. I can't remember if the plug is connected in the mirror or right when you take it off but the rest just comes apart with those 2 screws on the bottom once you get it off the car.
Green 2000 SVT #1166
mods-K&N open air filter & Custom heat shield, Custom y pipe and 30 in resonator,DMD, arm rest heightened
http://www.geocities.com/savinoss/Cars.html other cars-89 sable 197000 miles and still going-Wifes car 99 Mystique V6 5 spd