I have seen various suggestions regarding the wiring for this conversion.
Here is how I have dealt with it, as mentioned previously I have used an earth block from Screwfix.
This has been mounted in a small plastic box for insulation and the ends of the wires soldered before inserting into the block.
I know it doesn’t look too original, but once mounted it will be quite hard to see.
Still have to tidy up the spare black wire from the regulator box, the warning light wire.