Are these LED lights... I installed LEDs in my popup trailer ceiling lights and found out just a drop of water over the ON-OFF switch will turn on the LED lights... They don't draw enough current to need a strong make break contact like the ON-OFF switch would give...
Also light systems that have frame ground connections really do strange thing sometimes... A burned out shorted bulb or socket can do strange things to you...
I guess i would start tracing things out with a multimeter try to see what is going on...
Haven't played with any of the TC DOT safety lights circuit but on my truck 7-way connection I have one of these 7-WAY TEST modules that will plug into the 7-way socket and then I go through all of the truck safety light controls and make sure the truck side is not doing anything funny... Saves me alot of time knowing where the problem might be originated from...

Roy Ken