Did you look here?
http://forums.pelicanparts.com/porsche-911-technical-forum/1022018-flag-mirror-wires-tool-help.html
If yours are like mine, it takes a twist with a small needle nose to unlock the wires. I took off my mirrors for painting. Like for you, the tool did not work for me. Likely depends on the year of your car though. Another tool is mentioned in the link.