Rear fog light not working - what does this idiot try next ?

[Ant]

The Worlds worst mechanic is back, my car has told me to check my rear fog lights, so I did, it was not wrong the nearside one has given up the ghost.

I impressed myself by removing the black plastic slidy thing on the lower tailgate, then removed the offending fog light bulb, Swapped the bulb for a spare and it still did not work. So like a dope I put it all back together and looked online for a bulb holder (my thinking being if its not the bulb try the bulb holder next), then I remembered there is one on the other side, so I went and took it all apart again and swapped them over. Again the nearside one does not work.

So even I can now see that the bulb and the bulb holder are both OK, but what do I look/test next ?

By the way the reversing light on the nearside DOES work, so what am I looking at here ??

Is it the wiring ? and the black plug thing that carries the current to the unit.
Is it the actual light cluster ?

Any help, as always, is appreciated

[Horizon]

Could be a bad earth/ ground connection. You will need a multimeter to check to see if its a bad/ missing positive or ground connection. One that can read 12v DC.
Without a meter you will have a problem diagnosing the fault.

[Ant]

How about one of the screwdrivers with a light on the end ?? 
That's about as technical as I get