Installed a Burnsmoto USB plug for the Rally. I’ve installed the exact same kind of plug on 3 of my previous bikes and it has always worked very well.
The unit is as simple as it gets. It connects directly to 12 volt system and powers down to USB power requirements (DC 5V +/-0.25 and 2.1 amp max). This means once you find a source for aux power, just hook it up and you are good to go. The plug can also be connected directly to the battery if no aux power plug is available.
It comes with a mounting bracket, but I haven’t yet been able to find a place on any of the bikes to use it.
AThis time I zip tied the plug to the GPS bar (I’m calling it that from now on). It’s solid enough that I can’t push it down nor does it move up if I pull it. That said, it’s not 100% elegant solution. There is surprisingly little real estate behind the screen to mount stuff, but I have some ideas I will have to test out. I did put a mesh sleeve on the wires so they blend in with the others.
As for the actual source of power, I wired the USB plug to the socket found under the left front fairing (the black bit) (more here: https://honda250rally.com/2017/03/21/honda-250-rally-aux-power-source/)
Amazon has these: USB Weatherproof Charger Socket 2.1 Amp to Bare Wire
Some more photos for those thinking about mounting options on the dash. Edited the photos for clarity and details so they are intentionally a b it off.