You use a 12volt battery i assume..?
To be honest, i cant make head nor tail of your post mate...if you can, post a pic of the diagram.
But i'm pretty sure mines wired up as my post above and alls been good...
Edit - just re read your post, i get what you mean now (i think)
Yeah, you ground the leisure battery rather than have a negative wire from the leisure to the split
I'll have a look at mine in the morning and see which ports you need