GIVI TOPBOX BRAKE LIGHT HELP?

OK. I'm hopefully looking for another poor soul, who has fitted a GIVI 108 brake light to a GIVI 370 top box? The instructions are poor and not clear. 2 main problems exist:
1. The LEDs fit into the existing reflector. However the LEDs don't appear to fit through there reflector enough to allow the back of the unit to fit? See photos.
2. I am told to fit a grommet for the feed wire but the instructions are so unclear it's impossible to decide where?

Hoping someone else has suffered this before I start drilling and modifying things to the best I think! #GIVI #givibox #givi108 #givi370. #motorcycle #motorcyclemaintenance