All:
Thanks for the replies. I have mentioned some of the answers here and there elsewhere, but let me summarize again in case I missed anything.
The rollers have been removed, and the roller connection wires do not go anywhere. As a PS3 unit, it came with a pantograph/roller switch, which I removed. The pantograph directly feeds the PS3 board; there is no involvement of anything to do with rollers or their connections. Even if I missed something and shorted the roller wire with the outer rail (which I already confirmed is not the case), it wouldn't matter, as the 3rd rail on my system is completely dead, and disconnected back at the control stand. One can short the 3rd rail and outer rail during operation of trains, and nothing happens. The 3rd rail can power coaches, but that requires a manual plug-in at the control stand to enable, and I rarely use it. The system was specifically designed to make as little use of the 3rd rail as possible. As far as the coupler wires are concerned, I did think of that initially and checked them for nicks. I didn't find any, but as a confirmation, I disconnected the coupler on that truck completely, and there was still the same arcing on the next test. Perplexing.
It appears that the frame is becoming hot somehow, and that point on the truck is the 'point of least resistance'? I checked if there was any continuity between the pantograph and the metal in the shell, and then to the frame, and there was none. I didn't expect that anyway, as the pantograph is mounted to an area of the roof that is all plastic. Even if something was a miss there, why would it run with no problem for over two hours, then suddenly short out?
I have to be missing something, probably simple and obvious. I am even re-checking some of what I already did, just in case. Thanks again for the responses.
