Minecraft wiki entry for Redstone_Dust, associated text: If there is only one such adjacent redstone component, redstone wire configures itself into a line pointing both at the neighbor and away from it. If there are two or more such adjacent redstone components, redstone wire connects them in the form of a line, an "elbow", a "T", or a cross as needed. If there are no such adjacent redstone components, redstone wire configures itself into a plus sign, which can provide power in all four directions.