Everything in phase?
If it were me, and going on your description, I would first disconnect all TIU outputs to eliminate any downstream wiring issues. If the problem goes away you know where to look.
If you still see the high voltage, disconnect all other power sources and leave only the source feeding port 2. If you don't use aux power to power the TIU obviously you need to have fixed one powered, just leave all TIU outputs disconnected to the track. See if you still see the high voltage on output 2.