The cars originally came with wiring for a fog light on both sides, but r/h drive cars had a blanking tab over the bulb holder on the left hand side, and vice versa for l/h drive.
Many people broke the tab off and fitted a bulb in the other side to give then 2 rear fogs.
I'm on the look out for a Hella half smoked n/s rear with the tab intact if anyone knows to one.