When I bought my Mechman alternator the instructions said to wire it up that way but I mostly ignored that until I started having battery issue's but my batteries were both bad also when I replaced them I wired it up so both grounds are on the RVC seems to work better but no telling if it was just the batteries or not.Thanks, I'll check into that. I set mine up to factory specs, if I remember correctly the aux battery ground was to the back of the block. I seem to remember it being a real ***** to get to.