I would avoid using a scotchlock to splice into the wires already there, if you run a new wire down the A pillar to the fuse board behind the glovebox as others suggest you will find a couple of spare positions bottom left of the board one is permanant live and another ignition fed. Use a piggy back fuse connector to connect into the slot you choose, ignition fed is probably the best one to use.
https://www.ebay.co.uk/itm/2x-Standard-Add-A-Circuit-Fuse-Box-Holders-Piggy-Back-Adaptor-Car-ATO-ATC-ACU/322507617095?hash=item4b16f3b347:g:U7QAAOSwOMdZVLiG
Thats a link to a standard type fuse, there are mini versions so make sure you buy the correct size, think they are standard on Z4, more modern and Japenese cars tend to use the mini version.