ha ha this is one i always find funny as the pickup is simply a magnet with a thin copper wire around it as the the teeth pass it it chops the magnetic flux and induces a sharp ac wave/voltage in the copper wire.
the idea is to get the ecu phased to the engine.
if the wires are switched it offsets the phasing as the up peak would be down.
here is some pic's of a ford one as iirc there all the same