I think it was just a fluke, I know how hard it is to get the wires down to a license plate light when they are frenched in and keep them away from the tire. The next time I have the opportunity to work on it, I will remove the fender, glass a flexible tube in place for the wires and make everything quick disconnect so if there ever is an issue it can be handled without disassembly.
I imagine the previous rider rode the bike with the air pressure low to make the bike look good and the tire rubbed the metal plate creating enough heat to loosen anything that held the plastic light on. No big deal, just one of those things I did not know to look for. Randy built one heck of a bike with this one, everything is great, would like to see more of his creations, appears to be a first class builder and manufacture of parts for the conversion.
Bike rides and handles like a dream, it will be ridden, as a matter of fact my wife is seriously thinking about riding again so I may lose it to her.