iphone attachment to Commando

I have an Optimate flylead TM 71 to connect to a battery tender, and a selection of TM converter cables — most notably the O100-TM USB Charger, which includes an SAE connector.

Using these together I have connected satnavs and iPhones in the way that you suggest with zero problems. 

.............black is negative.    

I attached a Garmin satnav unit to my Commando some years ago. I installed the power unit inside the headlamp and ensured that it was isolated from any metalwork. The only issues was that the outer shield of the satnav connector was -ive and if it touched the handlebar when not actually connected to the satnav it would blow the fuse that I deliberately fitted. It may be worth installing a fuse somewhere in the power feed just to be on the safe-side. i phone connectors may be different of course ... .

If you are really concerned run the leads from the phone charger directly to the battery, positive to positive, with a fuse. Forget the polarity of the bike. The advantage of doing it this way is that you can charge the phone without the ignition on. No current will flow when the unit is removed from the holster. 

Don't bother with the iPhone.  Go for a ride on your Norton.  Look at the telephone when you reach your destination. 

Polarity of bike irrelevant.

Red positive

Black negative

no from me red positive + black to a earth or neg on battery 

If you fit a waterproof   ciggaret lighter socket you can plug into that , pump tyres and make tea , have a wander light for your tent or whatever. I have one on my 99. And panniers for all the accessories.