This is an "ignore the man behind the curtain" situation.
If you accept the procedure of rotating the switch to the "OFF" position for a few seconds every time you want to change the active siding then so be it. A possible benefit of Barry's suggestion to use the DCSRC would be have your lighted bumpers remain on while the man-behind-the-curtain (i.e., the DCSRC) is momentary attached to the yard power for the purpose of generating the watchdog to silence the new track. Otherwise the lighted bumper on the new active track would turn off during the interval when power is removed from TIU. I'm not sure that's what Barry had in mind but I figure he was proposing the DCSRC in addition to the existing passive-mode TIU which you'd obviously need to control your engines.
Anyway, I guess simplicity wins out. I was thinking it could be done with a bunch of capacitors to detect a change in the switch position and a 555-timer chip to detach the relay for a couple seconds to cycle power to the passive TIU. But during this interval the lighted bumper would turn off which could be confusing to the casual user if the lighted bumper is the only indicator of the active siding.
