This is a basic JavaScript I am trying to use in a platform so that when the player touches it, the level will change.
function OnTriggerEnter( other: Collider)
{
Application.LoadLevel("Level_2");
}
But nothing happens when the player touches the platform, no matter which collider is set to Trigger.

Is this on the platform, or the player? Do you have Level_2 defined in your build (and since you are using string, exactly named "Level_2"? If all that's setup and you still aren't getting the transition, your Trigger isn't firing - do you have layers configured? Typically a trigger has something like this in it if(other.tag == "Player") // do stuff so that a random thing hitting the trigger (ie not a Player) won't fire the event
– getyour411add a print or console.log statement to test if it is triggering, if not, do what getyour411 said. In addition i would add a rigidbody to the platform, and the player if it doesn't have one. things can get unpredictable if rigidbodies are not attached to the objects you want to detect collisions with.
– rednax20