I would check any additional cables coming from the battery, i got mine a couple of years ago & when i lifted the seat there were several redundant cables cut off under it, i also had to rewire the trailer & replace the lights as reflectors were tarnished inside.
If its drawing power from the battery with the ignition off its likely to be something directly connected to the battery.
Yes. This bike was like that when I first had it. Lots of wires (like a plate of spaghetti) going everywhere. One thing I have learned since having a 'Wing is 'parasitic drains' so I removed all extra wiring from the battery. I don't have anything extra connected to this at the moment. In fact, what I am attempting to do is familiarise myself with all the wiring that has been fitted, removing anything that is redundant and replacing all that needs to be replaced. Hence my reason for checking the trailer socket in the first instance!