There's an LED on the processor PCB that indicates which car is master (in the HHT also). Just turn off mainline to the current master car to force a switch. I would start looking at I/O's - HU and HD, T/B69... in other words find out when the car runs from 1 to 2 and has car calls ahead, do you have an up direction, call LED, UPSV etc. etc.
After re-reading your first post, does the COMS LED being on indicate a problem? I thought it was the COMF that is a COM failure. Unless I'm wrong because it's a car to car comm prob.
