This is very close to what I did in my E70 X5. I popped off the plastic housing that connects the rear view mirror to the windshield. There I determined which cable supplied the appropriate power (I think it was like 11.5 volts) and then spliced in my power cable to the V1. I put it just on the other side of the rear view miror (right side), as it allowed better fitment between sun shade, and adjustment of rear view mirror. Did the exact same thing in my 335. Works great.

BTW, can't believe how many times this V1 has saved my A$$. Haven't gotten 1 ticket since. I only wish I could disable X and K bands completely, and just listen for Ka and laser...