i'm going back a few years ago since i rewired my 56 - and its 4am here and dark out so i can't go look - but the purple wire is indeed the resistor bypass to deliver full voltage to the coil while cranking. it goes to that small terminal on the starter switch. it runs inside the cab to the ignition switch wiring and back out to the downstream terminal of the resistor. if i recall correctly, it is a strange wiring arrangement - but schematically it does provide +12v to the coil when cranking.
by the way, this is for the 235 6-cyl. the V8 is wired a little differently
