Doug, I think Doug L. has nailed it - there are a variety of MkIII wiring diagrams, but, looking under the dash, my hunch is that the purple wire either goes to the horn or to the high beam/low beam dip switch. Green White is RH flasher. That said, in one of the diagrams I am looking at (Haynes pg 201) there is a harness connector that has the purple and the green/white going through it ( but not the ignition) so it shouls (?) be plug and play. keep us posted.