Wondering if anyone can point me in the right direction, my side light on one side will not light up (drivers side 4x4 Saph. Cossie).

It's not the bulb or the bulb casing as I have tried it on anotherone, it's not the fuse so it's left me wondering what the hell it is, The bulb lights up when the fog light switch is turned on but dead otherwise (all other lights lightup ok)

Is there some kind of earth that could be stopping just the sidelight from coming on (the sidelight on the passenger side works perfectly btw) The warning light on the dash came on telling me there was a bulb out just after I booted it so the back end squotted a bit not sure if any wires can get snagged?