WIerd. I have double head K-Line Pacific set up. One of the engines came with a plastic Trainsounds tender and the other is just plastic. You plug the tender w/Trainsounds into the engine, like normal. Plugging it in has to do with the reverse light on the tender, plus it also makes the Trainsounds work. It won't work otherwise.
On the other engine I wanted to substitute a die cast Railsounds tender for the plastic. So I did. But the train starts normally and then pulls up abruptly. Halts. It will move again later or after you turn off all power for a few seconds, but run into the same problem in a few feet.
Here's the wierd part. The Railsounds tender merely being present and rolling somehow causes the other engine with the plug-in to switch into neutral (or reverse, I can't tell which) halting the whole train. Why would it do that? If you pull out the plug for the Trainsounds, it doesn't malfunction, but the Trainsounds doesn't work, either.