I have a rail with a T-junction. At the junction the user is given a choice of which direction to go. If they push a button they go one way, if they don't push the button they go the other way. My problem is the direction that the rail defaults to when using a button is the opposite of the direction I want it to go if you don't push anything. How can I reverse the default direction of the rail when the button is off?
If you want to get a little more complicated, you could use a
Not Gate. In a nutshell, a not gate is a logic gate which inverts a signal. Basically, if your lever is outputting a redstone signal, the not gate will not out put the signal.If a lever is in an off state, the not gate will out put a signal, achieving what you are asking.
A not gate is very simple to build. You only need to put a power source (lever, button, etc.) on a block. On any free side of the block (except the bottom face of course) you put a redstone torch. It's that simple. The redstone torch should be touching the rail, and when the lever/button/etc is flipped, the torch should turn off.
With this gate, the signal is inverted, therefore changing the default state of the lever/button.