MLU FORUM - 17 pdr Sight illumination gear

I have four different 17pdr manuals here along with the illustrated parts list,
Although the parts list has a very nice outline drawing of the Sight illumination box there is no description as to where it is positioned on the shield.
The box has four flat metal tabs protruding out from the base of the box that you would think gives some indication as the where it bolts to but after clambering over my gun leaves me non the wiser soooooooooooooo my question is ,can anyone shed any light (excuse the pun ) on this. :confused

Rob....................rnixartillery.