i unsolder and remove the white wire completely.
on all the magnetos i've seen, the blue is soldered to a tab on the top of the coil, the white on the bottom, and the black screws into a mounting bolt.
older motors used the white as a kill switch. i've never had a problem using it, but others claim burnt out mags and cdi's.
if you've found some use for a white wire, if the mag has a tab on the bottom you could probably solder it on.