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[GTW]

I recently purchased a head unit to put into a UK spec 07 320D. I used a “connects 2” harness to mate it to the wiring harness. There is a separate power lead that plugs into the fuse box for power but there is a problem: after the ignition is off for 15 minutes the fuse box has the power removed automatically as a way of protecting the charge of the car battery. This clever innovation is messing with my head (unit); every time I get in the car it has dumped any personal settings and is back to factory settings. Very annoying!
Have you met this issue before and do you have any bright ideas on how to solve it? Tapping into a ‘live’ elsewhere is proving difficult to achieve. I've looked through lots of threads and can't find a suitable fix.

Thanks in advance if you can help!