Minecraft wiki entry for Redstone_components, associated text: When placed, redstone dust configures itself to point toward adjacent redstone dust (at the same level or one level up or down), correctly-facing redstone repeaters and redstone comparators, and power components. If there is only one such neighbor, redstone dust forms a line pointing toward and away from that one neighbor (which can cause it to point toward blocks it wouldn't normally point toward). If there are multiple such neighbors, redstone dust forms either a line, an "L", a "T", or a "+". If there are no such neighbors, redstone dust forms a large directionless dot. Redstone dust does not automatically configure itself to point toward adjacent mechanism components, it must be arranged to do so.