It doesn't really matter. It'll work. To get the best setup, connect the wires like what Dell says. Then measure the signal strength in dbm. Then try swapping the antennas and measure the signal again. Choose the one that gives a better signal. If they're the same in every position, then it doesn't matter. I recently opened the bottom of my laptop to clean the fan and heatsink and I saw that mine has the black on Main and white on aux. I have the 7260N btw.
How can it not matter? Am I wrong in assuming that one post will be for 2.4ghz wifi & Bluetooth, while the other post will be for 5ghz.
Why doesn't Intel tell us which post is 2.4ghz and which post is 5ghz
The position of wireless antennas do not correspond to 2.4 and 5 GHz bands, single band adapters have two antennas too.
Intel® wireless adapters are meant to be professionally installed by Original Equipment Manufacturer technicians on certified systems only. We encourage contacting the respective system manufacturer (OEM) to determine the process for the appropriate hardware integration.