starter problems

[WILT]

The camper van [ mk 6 , 350/90 ] developed a strange fault towards the end of our last trip in that the batteries did not seem to charge when running but the cigar lighter voltage read out 14 v consistently whilst on the go. If we stopped for coffee or lunch it was touch and go whether it would start again. I had to resort to switching in the two batteries I use for the on board inverter that powers the fridge . I have had the batteries out and charged them and tested them with a dump tester and they are fine. If the batteries are trickle charged overnight on site using the on-board PSU the van starts better . Whlist investigating the batteries I disconnected and cleaned the earth under the drivers seat and noticed some sparking with nothing switched on. It appears there is a 250-300 milliamp drain and a relay [ no 30 ] in the passenger side dash area is firing when ever the batteries are connected .Is this door locking supply?