Second Radio board burned out in FastTrack O36 LH switch

The fact that you say the switch was "installed" on the layout, but not "fastened down" and worked great, but then failed only after fastening it down could be a clue as to what could be happening.

By "fastening down", I assume you mean screwing into the track. FT switches need to lie as flat as you can get them and even slight overtightening the screws can cause issues because you may be compressing or distorting an inside component against something else and causing a short. 

If the adjacent track sections screw down fine and there are no issues ("Fastened down the remaining track sections around it, worked great") then I would just leave the switch installed, but not screwed down, and hopefully, that will resolve the issue. It's not mandatory that every piece of track be screwed down. If the track is laid properly, a screw in every 3-4 sections, especially FT which is so stiff,  should be fine.

Richie C, thank you for responding.

Yes, that is what seems to be happening, i.e. a short of something internal, destroying the radio board. But, the BIG question is: should that happen!?

There is some type of "barrel" (forgive this non-mechanical engineer for not knowing the correct term) around the fasten down hole(s) of FasTrack , and I do not tighten them enough to distort the track, just snug up the wood screw "conical" section to the hole for it.

My layout is being built on plywood, so for the moment I will leave off the metal plate on the switch bottom, leave out another new radio board (until I figure out what could be shorting), and control the switch with an SC2 (besides the manual remote control).

'Til then...

Well…What’s on the top of the radio board that might touch the metal bottom plate when you tighten it down. I would have to be some metal showing on a resistor, etc. Then put a piece of black tape over that part…or better still, put a layer of black electrical tape or gorilla tape over the inside of the bottom metal plate where the radio board could touch it.