1. If you added the wrong number, it still worked.
The condition is a real possibilty concerning the past and the outcome is a fact known in the present. Usually, the first conditional is if + present + will, but I think this is classed as the first conditional because we are dealing with what is real. I'd be more than happy for anyone to correct this classification if they believe I'm wrong. ![Smile [:)]](/emoticons/emotion-1.gif)
2. If you added the wrong number, it would still work.
Technically speaking, this is the second conditional if + past + would. This statement could be said before the test as an imaginary scenario. In other words, the person in question has no intention of adding the wrong number.
If this statement were said after the test, then it would be a mixed conditional, as the condition is based on a real possibility, yet the result is unreal.