Did the T.B. 2 unit come with a 2 wire plug? Or did it come with just 2 wires? Usually they just plug-in to the circuit board. Or you can wire it like ROYBOY mentioned. To activate the whistle you will need to push the whistle button and it will play the grade crossing sequence(2 long, 1 short, 1 long), the bell is activated by the bell button on the transformer. If your transformer don't have both horn & bell features you can use a Lionel sound activation button sold separately and wire it in reverse for the bell. Or you can add a double pole double throw switch between the transformer and the track and reverse the track power to the track to get both the whistle and the bell feature.
Lee Fritz