After I ran my 2009 C70 through a car wash (has undercarriage wash as well)the electricals went nuts after about 20 mins when I left. Radio was on but would not turn off, warning lights of all kind went off, even the windshield wipers came on without the switch being on! Then as fast as it came it went away. Then did it again, then ok. Only did it one day. Now it has been two days with no issues. I just replaced the battery a month ago. It checked out ok. I bought the car from a guy in Myrtle beach. Would it be a battery cable corrosion issue or maybe a wet alternator? No clue!

 

sounds like an electrical issue, probably with water getting someplace it shouldn't. I am not sure if hardtop convertibles are the same as soft tops, but they don't recommend automatic car washes because the pressure can force water past the seals of the top and get electronics wet.

I'd check for we areas inside the trunk and body if it happens again.