A leak in your system causes the water pump to keep running... Before you say its bad close off the port going to the fresh water tank and see if the pump still stays running...
Your problem just might be a leak between the pump and the fresh water tank.
Even when I have NO WATER in the fresh water tank and I accidentally turn on the water pump it won't turn off... I have to add water to the tank to get it shut down...
Another problem I had was I have the winterizing switch with a short hose that goes down into the pink stuff. I left my switch setting to short hose and the pump stayed on when I turned it. Then I noticed what was wrong and switch to the fresh water tank and it shut off...
Roy Ken