Is there a way of getting the already-fitted 2nd rear fog light to work with the 1st that already works? It seems the European model XC60 (2018 on) has both fitted, but only 1 is connected.
Could I connect the 2nd myself??

 

Yes and then it would look like you have your brake lights on all the time - and cause some drivers to not notice when you DO put on the brakes.

When I see cars with the rear (or front) fog lights on when not needed - I guess they are just getting prepared for the fog! (middle of the day and sunny)

Most rear fog light users have no idea what they are and that they are even on.