If you have a mine-cart track system in your world and yo have the problem, "do I go left or right." After many failed attempts I have figured out how to build one;
You need dirt or grass
stone or stone brick
Step 1: Setting Up
OK, as the first picture shows you have a track going left and right. to start dig out 3 blocks( see 1st and 2nd pics)
place 3 powered tracks in the 1 by 3 hole you dug. make it look like the 1st pic.
Step 2: Do Some Digging
Dig out steps like the picture shows(later this month I'll make ms paint drawings to better illustrate.
next dig a 3 by 3 hole 3 blocks deep like the picture.
Step 3: The Box Switch
now for some redstone...build the box switch just like I did(Its easier if you do it exactly)
dig out steps like the 2nd pic and add redstone like the 3rd
Step 4: Connecting the Wires
Now all we have to do is control it look at the pics to see how it works. The missing tracks were removed to show you were to put the redstone.
Step 5: Cleaning Up
place dirt or grass like the picture.
add buttons on the front of the block and signs showing which way to go.
Here's how it works you pull up to the switch, the non powered track stops your cart in front of the buttons. you choose the left or right buttons. Without getting out of your cart the track switches to the direction you want and powers the track beneath you causing you to go.
please rate and comment and PM if you have questions.