I have six locomotives on my layout. Three have a single powered engine and I have set up as Engines on Legacy. I have three other locomotives which I have set up as Trains as there is more than one powered locomotive. The three that are set up as Engines run perfectly. The three that are set up as Trains run for a few seconds and then cause my ZW-L to short. In each case all of the cars are on the track properly and I can reset the transformer to eliminate the short. I can then run the Engines with no problem but all three of my Trains will short again. I am assuming I have set something up wrong but I believe I followed the manual. Can anyone give me some suggestions.