Morning all! I seem to have even more time on my hands than normal, so, and additional H'penny:
For the purposes of fitting an Acc. socket, others here are better informed as to whether Herr BMW had the foresight to include spare fused outputs from fuse box (?) Handy if he did. If not, it is simply a question of connecting suitable cabling, c/w inline fuse to your socket of choice.
I think there might be some confusion regarding relays.
Relays permit the safe 'switching' of high initial loads.
If a set of contacts are asked to switch too much current, they can weld shut or have bits blown-off the edges of the contacts (etc blah).
Normally then, 'heavy' items tend to be switched using relays, because the heavy contacts within the (appropriately selcted) relay are designed to handle the spikes and hi current present when this occurs.
Using relays allows the use of those nice little switches we have on our handle bars.
All those switches do is to pull-in a coil within the relay, which, again, is
doing to real 'switching'. Allowing also the use of those thin wires you see
going to and from your handle bar switches. Several tens of mili Amps instead many many Amps.
So. Back to your socket (get on with it!!), here, the switching bit (ie what relays do) is what you're doing when you plug into your acc. socket.
Nothing to worry about there (assuming app. useage).
If in doubt leave it out. Electrical fires are not good.
B.