I would connect to the bike's wiring harness wherever physical access was the easiest. Use best practices, a Posi-Tap makes a nice connection vs. randomly butchering the wiring. If you're careful to remove insulation without nicking any copper wires you can do an old-school soldered splice then cover it with self-amalgamating tape. Try to avoid normal electrical tape as it won't be as waterproof.

Connect the +12 wire to the fused side of any of the constant on fuse box wires or straight to the battery through an inline fuse.

I’ve not been able to power it at all, no matter what I do with the two leads?

The two power leads need +12V power and the ground lead needs to be connected to something connected to the battery (-) terminal. I would make damn sure the thing works before I did any modifications at all. Hook the ACC and +12V to the battery positive with jumper wires and the ground wire to the battery negative with a jumper wire. If it doesn't turn on it's broken.

If this is over your head, get help from someone experienced in wiring so you don't butcher up any wires in the bike's wiring loom.