It's actually surprisingly common for the internal crimps in Fastrack switches to develop high resistance. Why Lionel insists on depending on bent metal to conduct amps of electricity through the switches is a constant source of amazement to me! 
My first mission in this kind of situation is to remove the back of the Fastrack switch and solder all the crimped joints that carry any kind of current of signal to the switch. Here's my thread on what I did to the switches.
