Does anyone remember installing a Blend Mount/Uniden R7 on a 2007- 2009 Lexus RX 350. I want to hardwire my Uni R7 to the mirror. There are 7 slots in the mirror plug and 4 black wires going in so no discernable power line and ground. Does anyone happen to know which slot powers up when ignition is turned on and which slot is the ground. I realize this is a stretch asking about a 2009 Lexus RX 350. And yes I have a multimeter but I am still having trouble finding which slot is 12v and which is ground. Thanks in advance. You win a tee shirt if you answer correctly.