Moved my caravan a few feet last week using the Reich mover in order to get to a garden trailer, every thing worked as it should ( the battery has been on trickle charge for weeks.) when I then went to move the van back to its original position one of the movers had stopped working, I checked with a multi meter and I am getting Plus 12 volts one way and minus 12 volts the other so electrically things seem to be OK, Any Ideas wat the problem might be?