Permabanned
The ignition switch will be able to supply plenty of Amps, assuming it has a conventional switch, but poking a cable though a grommet in the bulkhead can't be very difficult. How many Amps does the rig draw at worst, th cigarette lighter might be able to supply it, check the fuse rating for the fag lighter, assuming it's got one of those of course.
Can-Bus can do "funny things" to supply points, like shut them down altogether if a module sees a current draw when it is not expecting there to be one. There'll probably be a current sensor(s) direct to one or both battery terminals, so you need to think when the rig will be drawing current and what will happen if power to it stops altogether. Things like memories or whatever. Modern Can-Bus can be a Royal PITA. Hazard light switch often stays live all the time, YMMV.
Can-Bus can do "funny things" to supply points, like shut them down altogether if a module sees a current draw when it is not expecting there to be one. There'll probably be a current sensor(s) direct to one or both battery terminals, so you need to think when the rig will be drawing current and what will happen if power to it stops altogether. Things like memories or whatever. Modern Can-Bus can be a Royal PITA. Hazard light switch often stays live all the time, YMMV.