Dome Brake Light fuse blowing

My dome light fuse has blown 3x now on my 71 Scamp. Can't see any signs of what is causing it, everything will be fine then out it goes. Needless to say my main concern is the brake lights. Okay so for the fun of it I replaced the brake light bulbs and everything seemed fine. I drove it around the development with the four ways on so I could see if the fuse would blow and it didn't. But when I turned the car off the four ways quit and the brake lights wouldn't work. Turned the four ways off and the brake light works.