Reverse switch on gearbox location

Hi all,

I have a reverse light problem on my Nissan Micra K12. There is no voltage to the reverse bulb holder when reverse is selected and the fuse is ok, so this leads me to the reverse switch. However I don't know the location of the reverse switch.

I have looked at the top of the gearbox and when reverse is selected, there are two pulleys which engage to wires. Is it on one of these pulley assemblies or am I looking in the wrong place?