Horn blaring and lights flashing

I’ve written about this before and failed to find the problem(s). The vehicle is a 2010 Honda Odyssey that I bought used. For the most part it’s been a good car but this horn honking and lights flashing is becoming annoying. I’ve learned that unplugging the hood latch switch is supposed to stop that. It’s been done and hasn’t done the horn blaring and lights flashing but recently in the last couple days it’s come back. The hood switch is still unplugged. There isn’t much information that I’ve found to addressing this issue. I wish that there were somewhere I could find electrical diagrams on security systems on vehicles and ground locations throughout this vehicle. One person opened up his door panel on his Honda and disconnected (removed) the door lock sensor to the drivers door. The dealer wants $300.00 just to diagnose this doesn’t give me much confidence when the manager said it may take hours to address the problem.
The horn honking seems to only happen when the weather is bad and it’s cold and wet outside. That battery is new about a month old. The terminals are clean with no corrosion. I’ve got a reading of 12.4 volts with key off and engine off. With key on engine off the battery drops to 11.9 volts. Not sure if this is normal. It starts and runs good otherwise. Any ideas?