Your wiring diagram reminds me of a little story :
so, I have the Flyer 326 Hudson from the mid 50's.
Roger Carp did a piece on this engine a few years back in "Focus on Classics", and he talked about all the fine features this engine has, including an electronic whistle. I was at a train show 3 years ago, and I picked up the whistle controller for cheap.
I was so excited to hear this whistle ! I downloaded the wiring diagram off the internet, and proceeded to make this girl sing !
upon completing a fairly convoluted wiring hookup, I pushed, and pushed that whistle button, and nothing happened. What could have gone wrong? Rechecked my wiring, everything is good.
Finally, I opened up the tender to discover some previous owner had removed the speaker !
your wiring diagram looks great, and I know you'll fair much better than I did !
Paul