Have a 2003 MINI base, not showing any water leaks but when it rains the Check Engine light on and off, ABS on and off, Tachometer on and off, Temp gauge goes to hot, running lights on and off, display on tachometer on and off, Brake indicator light on and off engine stumbles, all random, HELP!!

 

I'm new to MINI's but here is an idea. Check the battery box cover and seal above it to see if moisture is getting to the connectors on the ecu/pcm or whatever BMW calls it. If you have a corrosion issue it will also show as corrosion on the surfaces.