From what I've read the poor design on the brass contacts on Walthers SW1200 switcher and the easy potential for breakage of the contacts when removing the shell to access the motor, is common. I ordered a new walkway with intact contacts from Walthers. I also installed a Digitrax decoder since the model I had was Dcc ready. The decoder went in fine. The problem I am having is the failure to get a stable electrical connection again. When I put the walkway with contacts on the un-shelled body I get a connection and the engine runs. However once I connect the walkway to the shell and place on the body, there is nothing. Remove the shell, connection restored. Put back the plastic shell and nothing. My feeling is that somehow the shell (with new contacts) is shorting, but how or why since it is mainly plastic. Can any one offer some help?