Boy do I have a nice little problem, I have a 2000 coupe with a demon in its electrical system. Little while back it was the driver side window not going up or down all the time when I wanted it to. Then it seemed like ti spread to other areas such as horn, traction system service lights, now its where the gauges work on and off, service lights, the radio and all windows act up and don't always do what you want them to do? I have checked the battery connection, all the fuses and nothing.

Any clue what this could be? How to fix?

Did you check for any battery leakage? The cars computer is below the battery.

Also check in the passenger footwell for any moisture. The AC drain tube sometimes gets blocked and it will leak into the BCM located there. I know it's winter but your defroster uses the AC to dry the air...

Also, I doubt this is it BUT check all your grounds, it's tedious but well worth it.