Dan, there are no pw that I know of that are polarity sensitive, but whistle bells can be a pita at times.
That is to say the PW horn/whistle is operated by both a pos. or neg. offset in the ac wave. It's relay doesn't normally care which offset it sees.
A modern version would likely see the pos. offset and whistle. And if it sees a neg. offset it rings the bell instead. Bells usually take 2-3 seconds of holding to start to operate.
Some electronic whistles don't see a pw retifier disk well. A diode string addition works very well there. They can be set up to boost, or slow just slightly (1.5-3v)
In performance, the old tranformers added a voltage boost to compensate for the whistle motor. New equipment "turbo boosts" with 5 extra pw volts it doesnt really need.
Some "diode based"modern transformers will not blow all of my pw whistles and the engines slow greatly without the old 5v boost if they do work.
Your boost is likely intact on a ZW, good for all pw, and adding 1-4 heavy diodes to a 2 pos. temp, center off toggle can trigger the electronics without speed change. 2 each direction will give a 3v offset ea. when jumped in, I find it more reliable than a single diode each way and just a 1.5v offset. After loco rectification for a can motor, that big offset not really a concern. You might see some pulsing on an open frame; not detrimental, just not ideal. (PW whistle switch has stages as you turn the handle, high all, lowers after a split second to a lower mechanical holding voltage; I.e. it gets high offset/boost to get things moving then quickly lowers the values to just enough to keep its relay activated.)
Moving wires may effect relationships with other circuits, esp transformers/power packs, accessories taps, etc. and how you used them.
