There are no "spark plug wires" on the M, our ignitions are known as "coil over plug" or various other similar names, but what it comes down to is that there is no conventional high voltage spark plug wire, just two normal wires, I believe 16 gauge. One delivers ground to each of the six coil packs, and one 12volts, one of these beign switched by the pcm to control firing.
The coil which develops the high voltage required for a spark to travel from the electrode of the plug to ground mates directly to the spark plug, thereby eliminating the need of a special wire we call a "spark plug wire". This does a few good things for us like:
removing a costly part of routine maintenance in replacing wires
provides a more reliable means of getting our high voltage to the plug (no wires to fail or open)
MUCH LESS electromagnetic inductance induced into the vehicles electrical system and radiated in general under the hood. No matter how good plug wires are shielded for your typical car, they leak magnetic waves all over the place which are picked up by your radio and any other electronic devices.
1 or 2 mods.