Rear Passenger Side Light, twisting my melon, suggestions pls!!

My rear side light has always worked when it wanted so over the last couple of weeks I have tried, and so far failed, to rectify.
First off I found the bulb carrier for the side light partially broken, so have replaced and re fitted but still doesn't work, next up was buying a new bulb, again tried and failed (bulb works in another socket).

So just to recap, all other lights work except the rear passenger side light.

What else could it be chaps please, all suggestions welcome?    

could be corrosion on the bulb carrier, my mk1 cab was a pain for this had to really give em all a damn good buffing as combo of corrosion and overspray stopped em making good contact.

check you have voltage to the sidelight wire though its the grey/red and grey/black wires to the bulb carriers (cant recall off hand which is which)

Thanks for the suggestions, will give it a go, it doesn't feel serious as it has been working, its just gone pear shaped when I started meddling with it!!

Any suggestions on what to use to "buffer" the connestion's please?   

I have some wee wire brushes, but a bit of fine grade sandpaper will do the job you dont want to go mad just make sure all the metal contact points are nice and shiny. the tip contact inside the holder may be a little weak if so you can bend it upwards a bit so it makes stronger contact

Am fairly sure its a "power thing" now as I've rubbed the contacts so they are nice and shiney, strange as it worked before I started fiddling, need to get the connections tested next I think.