1965 Plymouth Valiant blown fuse

My dome light and cigarette lighter are on the same fuse. When I close the door I can replace the fuse without it blowing. When I open the door or push in the lighter it blows the fuse instantly. When the door buttons spring out when the door is opened it is designed to touch ground and the light turns on. I don't understand what is happening, I've traced down the wiring and tried it by disconnecting the dome light and trying the lighter it blows the fuse. I disconnected the lighter and the dome light connected and it blows the fuse. Any help you can give will be appreciated and help me understand this dalema thanks Sam