Battery/Accessory 12v power source F90/91 how does it work

[wski65]

I read on here that F90/91 is a spare battery/accessory power source.
I looked at it and there is a yellow 20amp mini fuse in that location.
It looks like it can be moved to the left or the right, leaving an open slot.
Does the position of the fuse dictate if the open slot is battery or accessory power?

 

[jsalbre]

It’s not spare, it’s the dash top 12v/lighter socket.

Yes, the position of the fuse dictates whether it’s ignition switched or always hot (battery).

 

[wski65]

Thank you