I've got a 2020 HiSun Sector HS550 and I'd like to know the same thing.
There are 2 connectors in back under my tilt bed\box hanging by the shock absorber, one is gray and the other is black.
I suspect the accessory switch goes to these but I do not know for sure.
One connector has heavier wires than the other.
The connectors are Molex brand, MX150 series.
The black one is connector configuration A and the gray connector is key option B, part numbers 334812201 and 334812202, respectively.
I found the connectors listed on eBay as Harley.
I'll be waiting to hear what the accessory switch goes to or for an electrical diagram.
Meanwhile, I'm going to go see what powers these two plugs.
Thanks,
Mike H
Meridian, Idaho