My Ford Galaxy locking and unlocking itself?

My 1999 T reg galaxy has had this problem for about a year on and off, where, ( It does seem after rain) the indicator lights flash and the car starts to madly lock and unlock itself until the battery goes dead. My hubby has checked all the connections in the door and sprayed with wd40. I have read here that its to do with the water and the windscreen , can anyone help as I dont want to get rid of her and I cant afford to send her to the garage for investigation , but its getting a bit much now.