Separate from the main fuses there will be an 'option connector' socket. If you can find it that will have a permanent live, an IGN pos 1(acc) and an IGN pos 2 pin.
Hopefully @steve_m might spot this and point you in the right direction as the permanent live pin often requires one of the existing fusebox empty slots to be 'populated'
It sounds complicated but is worth pursuing as the option connector pins are not affected by the starter motor afaik, mine aren't.
Multimeter job.