Paul,
Is your bike an ex Police bike, if so the source of switched power is easy. I am not a fan of breaking into wires and tapping into them as it can create problems later if not done properly. If it is a police bike, the have a look at the wiring diagram thats posted in the 1100 wiring area..
With regards the CB, some have had a problem with noise getting into the power wires, causing static/ whining in the audio out. There are a trick or two to reduce that.