For the life of me, I cannot find a ground back there. I tried the screw that connects the fusebox to the body; no go; connect ground to my door hinge, and all is good; I don't suppose anyone has a picture of a good ground behind the fuse box is?
Otherwise, I'm going to tap into the phone connection behind the console, as the 986 FAQ shows:
Permanently Installing a V1 Radar Detector - Porsche Boxster (986) FAQ
Looks like there is an accessible ground spot behind there...