Reply to "Can't find TIU when two or more power supplies power to the TIU"

 I use bulbs on my old TIU and just went thru this. I found a side of a switch was feeding thru that I thought was isolated. The bulb on the TIU output kept lighting until I cut that rail.

Cut the center rails on the branch lines after the switch. Your choice on exactly where. If it's easy to remove the pins and create a gap, do that.

Just so they don't back feed again to the other block.