My passenger side mirror does not move even though the motor seems to be working with the interior switch. It appears that something came detached from the back of the mirror. Any ideas? How can I take apart the mirror to investigate?

 

The tab for the right side mirror that is a hook for the spring broke on my 1999E and I had to make repairs.
If you look behind the mirror near the door you will See a rod that is clipped behind behind some tabs from the mirror painted shell.
un clasp them and the shell will slide back and allow access to the mechanism.