It is a rear fog light, it is only on the right side to indicate to drivers behind you in a thick fog that that is the far right of your car, thus being slightly to the left of the light, would mean that you are behind the car infront, not veering over to the otherside of the road...

I use it as a sort of brake light sometimes when cars are tailgating me. Aussie's don't know the difference they just see the red light come on and go, "shit, this cnuts breaking!" Works 9 times out of 10