Hi fargo400h and

to the Club !
There is already a USB Socket in the Glove Box, and this can easily be unclipped from the rear.
( It is designed for use by a device that fits inside the waterprroof glove box, and while possible,
it might not be the best solution to try and run an external cable into the glove box ).
Remove the Glove box by taking out the two screws ( one outside and one inside ) then lift the glove box
upwards and rearwards to disconnect the two front two pegs from their locating rubber mounts.
( Turning the handlebars fully to the side and squeezing the clutch lever makes it easier to remove ! )
To unclip the USB Socket, depress the side of the silver spring clip
and pull the Socket away from the Glove box.
You can then plug in your Mobile Phone cable ( Tape it up with electricians insulating tape
to stop it vibrating loose ), and this will not only provide power for your Phone, but if it is an iPhone,
then any Music files will be accessible to the Audio System which will identify it as an iPod

The Triumph Accessory Plug ( Part No. A9938122 ) that connects to the dedicated
Sat Nav power supply you mention, has two bare wires that can be connected to any device
needing a 12V power supply.
There are USB Power supplies available that could be connected up to the NAV Power Supply,
or directly to the Main Battery, that will reduce the Trophy 12V down to the 5V used by USB devices,
such as this one ( on eBay ) here :
Waterproof USB socket motorcycle motorbike 12v 2.1A hardwired connect to battery( I have no affiliation or any other association with the Seller ).
Cheers

