My neighbour was widowed a couple years ago and left with a big class A that she knows little about. Decided she needed new coach batts so had her neighbour on other side swap them out for her. Problem was he reconnected them backwards and blew every fuse in the coach. Took another guy who was an electrician days to figure out what had happened and replace all the fuses. She was lucky that was all it took to fix. Could have been much worse.