Probably easiest to identify the largest fuse capacity in the fuse box, most of the fuse box will only be on when the ignition is on (you can check this with a multimeter) then wire it directly or using a connector that taps into a wire coming from that fuse. Bear in mind they can pull a lot of current (in bike terms) so they can blow 12v aux socket fuses anyway.
Probably easiest to identify the largest fuse capacity in the fuse box, most of the fuse box will only be on when the ignition is on (you can check this with a multimeter) then wire it directly or using a connector that taps into a wire coming from that fuse. Bear in mind they can pull a lot of current (in bike terms) so they can blow 12v aux socket fuses anyway.