A friend of mine is getting back into modeling and has locomotives from both brands. Question is why does he have to reverse the power feed wires to the rails to blow the whistles? He is using a Lionel transformer and the Lionel whistles work fine, but he has to reverse the wires to get the K-Line whistle to blow.
The signal to blow the whistle is a small positive DC voltage on the center rail, relative to the outside rails. Both old and new Lionel transformers work this way (with the transformer connected to the track as Rob described above). If the ZW transformer has been modified by replacing the copper-oxide rectifiers by silicon diodes, the diodes may have been installed wrong. The Lionel schematic diagrams all show the diodes backwards. Older locomotives (those with whistle relays) would not have cared about the polarity and would have blown the whistle either way, but newer ones require the positive center rail.
Armed with the above information, I went down this afternoon and tried all of his locos out. With the ZW wired as Rob suggested, the K-Line and the pre and post 70 Lionel whistles sounded, however the post 70 Lionel RS-3 horn would not, it only surged when the botton was pushed. The horn would sound when the common was on the center rail, so it does function.
Is this just a reversed wire to the horn unit situation or is there more of a problem?