Sigma Rear Lights

Can anyone please confirm the function of the red rear light on drivers side below the tail/stop light. I always presumed it was a parking light but when activating these at ignition swith as per handbook get both tail lights on. It may not be working as I came to it investigating why the rear number plate lights not working. Have checked bulbs, connections etc but appears to have no live feed. Service man wants to cut off rear bumper/skirt to trace wiring which I'm reluctant to do. In my opinion should be easier to tap into an alternative live feed. All ideas welcome and appreciated.

Rear fog light ?

Concure with Willy and Pete, rear fog lamp,only used it twice when I had my Sigma.
Boaby

Many thanks for the lead chaps, it is indeed a rear fog lamp. Operated by a manual switch on drivers centre console when head or side lights on. Threw me completely when no front fog lights are fitted!!! I can't think I'll ever use it here so am considering using feed to fix my faulty number plate light.

I guess you would need to be sure that it will pass whatever the equivalent of the MOT is in NZ - it would be a fail in the UK if disconnected.

Would it really be easier to use that to feed your number plate light, rather than just taking a wire from one of the rear sidelights instead? It strikes me as being significantly harder, but I don't have a mental picture of exactly how the rear wiring is laid out on a Sigma.

Good points Mojo. I don't think the MOT would be an issue as the examiner would'nt know it was disconnected, and certainly rear fog lights are not a requirement here. Ironically I once nearly got a fail because the examiner thought it was an additional brake light, which apparently, if fitted must work. Suggested what I then honestly thought, that it was a parking light popular in the UK for on-street parking, and he accepted that.
I agree that it makes more sense to tap into a tail light but with my limited understanding of complicated wiring arrangements ( 'canbus' and the like) made me scared of that.   
Your comments are appreciated, thanks.