Tom Tom rider hard wire

Hi all this is my first post here, hello. I've set aside tomorrow for wiring up my Tom Tom rider v5 sat nav. After trawling the forums for how to wire it in I've not come up with anything solid. My dad is helping me and it a lot more electrically minded than me, thank god. He's thinking of wiring it into the rear light live. Now people have said online it needs its own relay and fuse, but were thinking the rear light will have a small enough fuse to deal with any dangers posed. It seems a pretty clear run from the front under the tank to the side panel that the wire runs into.
Any extra help would be appreciated. Thanks
Simon

Hey, I'm pretty sure mines wired to the rear light live. I don't remember my mate adding anything extra when he fitted it.