https://z4-forum.com/forum/viewtopic.php?t=73905 (although I'd suggest not using scotch locks personally.)
I ran mine (Garmin hardwired kit) down to the fuse box behind the glove box, took ignition from F2 and permanent live feed from F3 and used a ground nut nearby to ground it. Top connector in a fuse slot is the "hot" side.