depends on how you want it to run. purple should be always on. then it will have power when the bike if off. looking at the diagram, second wire should be blue. that should be key on power. then it will cut on & off with the key.
I ran my gps power under the tank and tied it to the accessory lights plug and used the red w/ blue wire for power (key on power) and black for ground. this was before I installed the PC-8.