I highly recommend invisicord:
Invisicord Products Home Page
For $15 you can hardwire your radar detector in less than 5 minutes. Just unplug the wiring harness from your mirror by pressing down on the top of the clip with a screwdriver while pulling it out.
The wiring for the mirror is:
black/red - switched power
yellow - always on power
black - ground
so plug the yellow wire of the invisicord into the harness where the black/red wire is. Plug the black invisicord into the harness where the black wire is. Plug back in the harness and you are done!
Here are a couple more pics:
The bracket I bought is real nice as well. Made of aluminum and well designed mount to the visor post. Here is an outside pic (was tough through the windshield and will try again in different lighting.)
Custom Made Connecting Mount for Radar Detector on 350Z and other Cars
Could someone verify whether non-Homelink mirrors have power or not?