I had left the wingtip extension overnight with some epoxy filler which needed to dry. I had previously applied beeswax to the wingtip so that the extension would come off, after the epoxy had dried to shape.
A mounting bracket fits on the end and the light unit attaches to the bracket. See Picture 1. I had to pull a wire and another string through the length of the wing. A bit nerve-wracking, but the string didn't break ;-) You can see spade connectors on the wire I pulled through, and on the earth strap.
The plans call for Molex connectors, but I could not find Molex crimpers for less than £250, so I went for spade connectors that I had "in stock".
Last job was to apply goop around the periphery of the extension to keep the water out. A fun day's work, for a change.