Unfortunately, someone interested in doing this won't read through to the end, and the OP probably isn't around any longer to update his original post. Nissan is no longer providing 12V to the mirror, so any product that taps into the plug WILL NOT OPERATE a radar detector.
I tried without success to install the MirrorTap harness, and even took it to a car audio shop to make sure. There is only 0.3V going to the mirror on newer Zs. Your only reasonable option to hardwire a radar detector is by piggybacking onto the radio fuse. Here's a DIY detailing this installation:
DIY: How to Hardwire a Dash Cam or Radar Detector