so, for anyone that is interested, (and anyone who couldn't find the information anywhere else from searching) I successfully, and relatively easily, hard wired my brodit phone mount to my new T6. I drilled two holes: one in the brodit mount itself, and one on the inside of the air vent, then ran a cable down to the fuse box, where i found a perfectly good earth spot tucked up above the fuses.
1. Took facia off with bike levers (and fingers) and the little plastic tool Brodit sent, then fed the usb cable through to the fuse box (i started with a bike brake cable housing, then once through taped the USB cable to it to pull it back.
It runs from the right had side of the radio down (and i easily fed it along the top of the raido)
I then drilled these bits....(12mm)..... and put the usb though (it was fiddly getting the usb through the air vent, i had to push it though from the other side with a pencil)
Fascia almost back on....
i then used a piggy back fuse thing and connected the usb (with the brodit hard wire kit) to fuse for the rear wash wipe (so connected to the ignition), and then went on a quest for an earth.
I tried this (found on this site) but it didn't work:
Then i spotted another place just above the fuse grabber thing, and tried that, and hey presto, we have power:
here is the final view of the fuse box:
all the cables easily tucked down there to the right.