There is no instruction manual with your hitch kit :?

Some people get a light socket extension, plug it into the light socket and
the wires are right there to plug into the hitch kit ... stringing them out
the boot.  No need to strip wires or cut into them that way.  When done
towing, then just take out the socket extension and replace the factory
system as before.

There is also a wiring schematic in the BMW shop manual for your vehicle.

sumbuddie hopes this helps