I thought a while about wiring in to the ignition or tail light, even bought a wee relay, in the end I didn't bother and wired GPS, Starcom and socket direct to battery.
Happy that I did, the starcom looks after itsself when helmet not connected, quite handy that GPS will power up and find satellites before bike is on (and draws no power when unit is not in its mount) and I haven't accidently left anything in the socket yet....

thanks for the info and the link page is a great help pics to follow 8)

It does matter. The center is positive.