Hi Petski2
Wire from positive of van battery--20 amp fuse---split charge relay--earth from negative on van battery onto chassis---wire from aux on relay --20 amp fuse--positive onto wfp battery---earth from negative on wfp battery to chassis?
The wiring description sounds correct. Its sounds as though you have one of the 'new' intelligent split charger relays that are able to identify the sate of charge of both batteries (vehicle and leisure) and give priority to the vehicle battery over the secondary leisure battery.
The split charger relay I have in my van has a 'third' wire , connected to the alternator charging warning light circuit in my case to activate the relay. This means that the relay is only activated when the engine is running, which is the system most caravan setups use. As mine is just a relay, priority charging goes to the flattest battery ( least resistance) but I have never had a flat van battery although I have sometimes run my leisure battery flat.
I can connect a volt meter across the battery and see the needle rise when the engine is started, indicating the battery is being charged. We also have a small battery charger which we use to top the leisure batteries up as we do very little mileage. It has a light that is red, but when the battery is fully charged it turns green. That red light turns green the moment I start the engine so I occassionally use that to check that everything still works.
Spruce