After a couple of false starts the sat nav is now permanently wired to a key switched circuit. Thanks for the tip James about piggy back fuse taps. An added benefit to the job is having less than a foot of wire on show above the dash, so it looks far tidier.
I use the cigarette lighter outlet for a satnav in my A3 Sportback and was surprised to find the outlet is live even when the ignition is off, leading to the possibility of draining the battery if I am not careful. Is this normal?