Lighting cable in dash
Someone recently PM'd me to know how I ran a USB cable 'under the dash' to keep my iPhone mount setup as clean as possible
Here's modest attempt to provide a DIY (I did not document the install when I did it):
Remove the centre dashboard air vents & trim and the radio/ac control panels as explained in the first 1:30 min of this video (no need to go any further!):
Remove the centre console trim with the iDrive controller (pull gently, only clips):
and unclip the USB connector in the armrest compartment. The USB cable will come underneath and it is cleaner to unplug the female USB connector from the trim, connect it to your cable and put the trim back in place so that the USB cable stays out of sight:
At this point, you only need to run a black (good quality) USB-lightning cable
I tried to represent the path followed by the cable on the following stock picture. The only tricky part is to get the cable from the centre console to the passenger footwell. Once it is done, you just tuck the cable under the the passenger side of the center console trim and make it re-emerge at some point around the iDrive connector. You then push it under the armrest compartment. With the trim pice surrounding the USB connector removed, you can easily access your cable and connect it.
It is all a lot easier than it seems. Just do not rush things and use trim tools to avoid scratching or breaking the trim parts you are removing.